text:
Gestation

Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time, for example in a multiple birth.

The time interval of a gestation is called the gestation period. In obstetrics, gestational age refers to the time since the onset of the last menses, which on average is fertilization age plus two weeks.

Mammals
In mammals, pregnancy begins when a zygote (fertilized ovum) implants in the female's uterus and ends once the fetus leaves the uterus during labor or an abortion (whether induced or spontaneous).

Humans
In humans, pregnancy can be defined clinically or biochemically. Clinically, pregnancy starts from first day of the mother's last period. Biochemically, pregnancy starts when a woman's human chorionic gonadotropin (hCG) levels rise above 25 mIU/mL.

Human pregnancy can be divided into three trimesters, each approximately three months long: the first, second, and third trimester. The first trimester is from the last menstrual period through the 13th week, the second trimester is 14th–28/29th week, and the third trimester is 29/30th–42nd week. Birth normally occurs at a gestational age of about 40 weeks, though it is common for births to occur from 37 to 42 weeks. Labor occurring prior to 37 weeks gestation is considered preterm labor and can result from multiple factors, including previous preterm deliveries.

Prenatal care is important for the maintenance of a healthy pregnancy and surveillance of related complications. In high-income countries, prenatal care typically involves monthly visits during the first two trimesters, with an increasing number of visits closer to delivery. At these visits, healthcare providers will evaluate a variety of parental and fetal metrics, including fetal growth and heart rate, birth defects, maternal blood pressure, among others.

After birth, health care providers will measure the baby's weight, vital signs, reflexes, head circumference, muscle tone, and posture to help determine the gestational age.

Various factors can influence the duration of gestation, including diseases in pregnancy and adequate prenatal care. The rates of morbidity and pre-existing diseases that predispose mothers to life-threatening, pregnancy-related complications in the United States are increasing. Inaccessibility of prenatal care may partially explain this ongoing disparity.

Non-mammals
In viviparous animals, the embryo develops inside the body of the mother, as opposed to outside in an egg (oviparity). The mother then gives live birth. The less developed form of viviparity is called ovoviviparity, in which the mother carries embryos inside eggs. Most vipers exhibit ovoviviparity. The more developed form of viviparity is called placental viviparity; mammals are the best example, but it has also evolved independently in other animals, such as in scorpions, some sharks, and in velvet worms. Viviparous offspring live independently and require an external food supply from birth. Certain lizards also employ this method such as the genera Tiliqua and Corucia. The placenta is attached directly to the mother in these lizards which is called viviparous matrotrophy.

Ovoviviparous animals develop within eggs that remain within the mother's body up until they hatch or are about to hatch. It is similar to viviparity in that the embryo develops within the mother's body. Unlike the embryos of viviparous species, ovoviviparous embryos are nourished by the egg yolk rather than by the mother's body. However, the mother's body does provide gas exchange. The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother.

The fish family Syngnathidae has the unique characteristic whereby females lay their eggs in a brood pouch on the male's chest, and the male incubates the eggs. Fertilization may take place in the pouch or before implantation in the water. Included in Syngnathidae are seahorses, the pipefish, and the weedy and leafy sea dragons. Syngnathidae is the only family in the animal kingdom to which the term "male pregnancy" has been applied.

title: Gestation


text:
Gamma function

In mathematics, the gamma function (represented by $Γ$, the capital letter gamma from the Greek alphabet) is one commonly used extension of the factorial function to complex numbers. The gamma function is defined for all complex numbers except the non-positive integers. For every positive integer $n$, $$\Gamma(n) = (n-1)!\,.$$

Derived by Daniel Bernoulli, for complex numbers with a positive real part, the gamma function is defined via a convergent improper integral:

$$ \Gamma(z) = \int_0^\infty t^{z-1} e^{-t}\text{ d}t, \ \qquad \Re(z) > 0\,.$$

The gamma function then is defined as the analytic continuation of this integral function to a meromorphic function that is holomorphic in the whole complex plane except zero and the negative integers, where the function has simple poles.

The gamma function has no zeros, so the reciprocal gamma function $1⁄Γ(z)$ is an entire function. In fact, the gamma function corresponds to the Mellin transform of the negative exponential function:

$$ \Gamma(z) = \mathcal M \{e^{-x} \} (z)\,.$$

Other extensions of the factorial function do exist, but the gamma function is the most popular and useful. It is a component in various probability-distribution functions, and as such it is applicable in the fields of probability and statistics, as well as combinatorics.

Motivation

The gamma function can be seen as a solution to the interpolation problem of finding a smooth curve $$y=f(x)$$ that connects the points of the factorial sequence: $$(x,y) = (n, n!) $$ for all positive integer values of $$n$$. The simple formula for the factorial, $x! = 1 × 2 × ⋯ × x$ is only valid when $x$ is a positive integer, and no elementary function has this property, but a good solution is the gamma function $$f(x) = \Gamma(x+1) $$.

The gamma function is not only smooth but analytic (except at the non-positive integers), and it can be defined in several explicit ways. However, it is not the only analytic function that extends the factorial, as one may add any analytic function that is zero on the positive integers, such as $$k\sin(m\pi x)$$ for an integer $$m$$. Such a function is known as a pseudogamma function, the most famous being the Hadamard function.

A more restrictive requirement is the functional equation which interpolates the shifted factorial $$f(n) =  (n{-}1)! $$ : $$f(x+1) = x f(x)\ \text{ for any } x>0, \qquad f(1) = 1.$$

But this still does not give a unique solution, since it allows for multiplication by any periodic function $$g(x)$$ with $$g(x) = g(x+1)$$ and $$g(0)=1$$, such as $$g(x) = e^{k\sin(m\pi x)}$$. One way to resolve the ambiguity is the Bohr–Mollerup theorem, which shows that $$f(x) = \Gamma(x)$$ is the unique interpolating function over the positive reals which is logarithmically convex (super-convex), meaning that $$y = \log f(x) $$ is convex (where $$\log$$ is the natural logarithm).

Main definition
The notation $$\Gamma (z)$$ is due to Legendre. If the real part of the complex number $z$ is strictly positive ($$\Re (z) > 0$$), then the integral $$ \Gamma(z) = \int_0^\infty t^{z-1} e^{-t}\, dt$$ converges absolutely, and is known as the Euler integral of the second kind. (Euler's integral of the first kind is the beta function. ) Using integration by parts, one sees that: $$\begin{align} \Gamma(z+1) & = \int_0^\infty t^{z} e^{-t} \, dt \\ &= \Bigl[-t^z e^{-t}\Bigr]_0^\infty + \int_0^\infty z t^{z-1} e^{-t}\, dt \\ &= \lim_{t\to \infty}\left(-t^z e^{-t}\right) - \left(-0^z e^{-0}\right) + z\int_0^\infty t^{z-1} e^{-t}\, dt. \end{align}$$

Recognizing that $$-t^z e^{-t}\to 0$$ as $$t\to \infty,$$ $$\begin{align} \Gamma(z+1) & = z\int_0^\infty t^{z-1} e^{-t}\, dt \\ &= z\Gamma(z). \end{align}$$

We can calculate $\Gamma(1)$: $$\begin{align} \Gamma(1) & = \int_0^\infty t^{1-1} e^{-t}\,dt \\ & = \int_0^\infty e^{-t} \, dt \\ & = 1. \end{align}$$

Thus we can show that $$\Gamma(n) = (n-1)!$$ for any positive integer $n$ by induction. Specifically, the base case is that $$\Gamma(1) = 1 = 0!$$, and the induction step is that $$\Gamma(n+1) = n\Gamma(n) = n(n-1)! = n!.$$

The identity $\Gamma(z) = \frac {\Gamma(z + 1)} {z}$ can be used (or, yielding the same result, analytic continuation can be used) to uniquely extend the integral formulation for $$\Gamma (z)$$ to a meromorphic function defined for all complex numbers $z$, except integers less than or equal to zero. It is this extended version that is commonly referred to as the gamma function.

Alternative definitions
There are many equivalent definitions.

Euler's definition as an infinite product
For a fixed integer $$m$$, as the integer $$n$$ increases, we have that $$\lim_{n \to \infty} \frac{n! \, \left(n+1\right)^m}{(n+m)!} = 1\,.$$

If $$m$$ is not an integer then it is not possible to say whether this equation is true because we have not yet (in this section) defined the factorial function for non-integers. However, we do get a unique extension of the factorial function to the non-integers by insisting that this equation continue to hold when the arbitrary integer $$m$$ is replaced by an arbitrary complex number $$z$$,

$$\lim_{n \to \infty} \frac{n! \, \left(n+1\right)^z}{(n+z)!} = 1\,.$$ Multiplying both sides by $$(z-1)!$$ gives $$\begin{align} \Gamma(z) &= (z-1)! \\[8pt] &= \frac{1}{z} \lim_{n \to \infty} n!\frac{z!}{(n+z)!} (n+1)^z \\[8pt] &= \frac{1}{z} \lim_{n \to \infty} (1 \cdots n)\frac{1}{(1+z) \cdots (n+z)} \left(\frac{2}{1} \cdot \frac{3}{2} \cdots \frac{n+1}{n}\right)^z \\[8pt] &= \frac{1}{z} \prod_{n=1}^\infty \left[ \frac{1}{1+\frac{z}{n}} \left(1 + \frac{1}{n}\right)^z \right]. \end{align}$$ This infinite product, which is due to Euler, converges for all complex numbers $$z$$ except the non-positive integers, which fail because of a division by zero. Intuitively, this formula indicates that $$\Gamma(z)$$ is approximately the result of computing $$\Gamma(n+1)=n!$$ for some large integer $$n$$, multiplying by $$(n+1)^z$$ to approximate $$\Gamma(n+z+1)$$, and using the relationship $$\Gamma(x+1) = x \Gamma(x)$$ backwards $$n+1$$ times to get an approximation for $$\Gamma(z)$$; and furthermore that this approximation becomes exact as $$n$$ increases to infinity.

The infinite product for the reciprocal $$\frac{1}{\Gamma(z)} = z \prod_{n=1}^\infty \left[ \left(1+\frac{z}{n}\right) / {\left(1 + \frac{1}{n}\right)^z} \right]$$ is an entire function, converging for every complex number $z$.

Weierstrass's definition
The definition for the gamma function due to Weierstrass is also valid for all complex numbers $z$ except the non-positive integers: $$\Gamma(z) = \frac{e^{-\gamma z}} z \prod_{n=1}^\infty \left(1 + \frac z n \right)^{-1} e^{z/n},$$ where $$\gamma \approx 0.577216$$ is the Euler–Mascheroni constant. This is the Hadamard product of $$1/\Gamma(z)$$ in a rewritten form. The utility of this definition cannot be overstated as it appears in a certain identity involving pi.

Equivalence of the integral definition and Weierstrass definition

By the integral definition, the relation $$\Gamma (z+1)=z\Gamma (z)$$ and Hadamard factorization theorem, $$\frac{1}{\Gamma (z)}=ze^{c_1 z+c_2}\prod_{n=1}^\infty e^{-\frac{z}{n}}\left(1+\frac{z}{n}\right), \quad z\in\mathbb{C}\setminus \mathbb{Z}_0^-$$ for some constants $$c_1,c_2$$ since $$1/\Gamma$$ is an entire function of order $$1$$. Since $$z\Gamma (z)\to 1$$ as $$z\to 0$$, $$c_2=0$$ (or an integer multiple of $$2\pi i$$) and since $$\Gamma (1)=1$$, $$\begin{align}e^{-c_1}&=\prod_{n=1}^\infty e^{-\frac{1}{n}}\left(1+\frac{1}{n}\right)\\&=\exp\left(\lim_{N\to\infty}\sum_{n=1}^N \left(\log\left(1+\frac{1}{n}\right)-\frac{1}{n}\right)\right)\\&=\exp\left(\lim_{N\to\infty}\left(\log (N+1)-\sum_{n=1}^N \frac{1}{n}\right)\right)\\&=\exp\left(\lim_{N\to\infty}\left(\log N+\log \left(1+\frac{1}{N}\right)-\sum_{n=1}^N\frac{1}{n}\right)\right)\\&=\exp\left(\lim_{N\to\infty}\left(\log N-\sum_{n=1}^N\frac{1}{n}\right)\right)\\&=e^{-\gamma}.\end{align}$$ Whence $$c_1=\gamma+2\pi i k$$ for some integer $$k$$. Since $$\Gamma (z)\in\mathbb{R}$$ for $$z\in\mathbb{R}\setminus\mathbb{Z}_0^-$$, we have $$k=0$$ and $$\frac{1}{\Gamma (z)}=ze^{\gamma z}\prod_{n=1}^\infty e^{-\frac{z}{n}}\left(1+\frac{z}{n}\right),\quad z\in\mathbb{C}\setminus\mathbb{Z}_0^-.$$

Equivalence of the Weierstrass definition and Euler definition

$$\begin{align}\Gamma (z)&=\frac{e^{-\gamma z}}{z}\prod_{n=1}^{\infty}\left(1+\frac{z}{n}\right)^{-1}e^{z/n}\\&=\frac1z\lim_{n\to\infty}e^{z\left(\log n-1-\frac{1}{2}-\frac{1}{3}-\cdots-\frac{1}{n}\right)}\frac{e^{z\left(1+\frac{1}{2}+\frac{1}{3}+\cdots+\frac{1}{n}\right)}}{\left(1+z\right)\left(1+\frac{z}{2}\right)\cdots\left(1+\frac{z}{n}\right)}\\&=\frac1z\lim_{n\to\infty}\frac{1}{\left(1+z\right)\left(1+\frac{z}{2}\right)\cdots\left(1+\frac{z}{n}\right)}e^{z\log\left(n\right)}\\&=\lim_{n\to\infty}\frac{n!n^z}{z(z+1)\cdots (z+n)},\quad z\in\mathbb{C}\setminus\mathbb{Z}_0^-\end{align}$$ Let $$\Gamma_n(z)=\frac{n!n^z}{z(z+1)\cdots (z+n)}$$ and $$G_n(z)=\frac{(n-1)!n^z}{z(z+1)\cdots (z+n-1)}.$$ Then $$\Gamma_n(z)=\frac{n}{z+n}G_n(z)$$ and $$\lim_{n\to\infty}G_{n+1}(z)=\lim_{n\to\infty}G_n(z)=\lim_{n\to\infty}\Gamma_n(z)=\Gamma (z),$$ therefore $$\Gamma (z)=\lim_{n\to\infty}\frac{n!(n+1)^z}{z(z+1)\cdots (z+n)},\quad z\in\mathbb{C}\setminus\mathbb{Z}_0^-.$$ Then $$\frac{n!(n+1)^z}{z(z+1)\cdots (z+n)}=\frac{(2/1)^z(3/2)^z(4/3)^z\cdots ((n+1)/n)^z}{z(1+z)(1+z/2)(1+z/3)\cdots (1+z/n)}=\frac{1}{z}\prod_{k=1}^n \frac{(1+1/k)^z}{1+z/k},\quad z\in\mathbb{C}\setminus \mathbb{Z}_0^-$$ and taking $$n\to\infty$$ gives the desired result.

General
Besides the fundamental property discussed above: $$\Gamma(z+1) = z\ \Gamma(z)$$ other important functional equations for the gamma function are Euler's reflection formula $$\Gamma(1-z) \Gamma(z) = \frac{\pi}{\sin \pi z}, \qquad z \not\in \Z$$ which implies $$\Gamma(z - n) = (-1)^{n-1} \; \frac{\Gamma(-z) \Gamma(1+z)}{\Gamma(n+1-z)}, \qquad n \in \Z$$ and the Legendre duplication formula $$\Gamma(z) \Gamma\left(z + \tfrac12\right) = 2^{1-2z} \; \sqrt{\pi} \; \Gamma(2z).$$

Proof 1

We can use Euler's infinite product $$\Gamma(z) = \frac1z \prod_{n=1}^{\infty} \frac{(1+1/n)^z}{1 + z/n}$$ to compute $$\frac{1}{\Gamma(1-z)\Gamma(z)} = \frac{1}{(-z)\Gamma(-z)\Gamma(z)} = z \prod_{n=1}^{\infty} \frac{(1-z/n)(1+z/n)}{(1+1/n)^{-z}(1+1/n)^{z}} = z \prod_{n=1}^{\infty} \left(1 - \frac{z^2}{n^2}\right) = \frac{\sin \pi z}{\pi}\,,$$ where the last equality is a known result. A similar derivation begins with Weierstrass's definition.

Proof 2

First we prove that $$I=\int_{-\infty}^\infty \frac{e^{ax}}{1+e^x}\, dx=\int_0^\infty \frac{v^{a-1}}{1+v}\, dv=\frac{\pi}{\sin\pi a},\quad a\in (0,1).$$ Consider the positively oriented rectangular contour $$C_R$$ with vertices at $$R$$, $$-R$$, $$R+2\pi i$$ and $$-R+2\pi i$$ where $$R\in\mathbb{R}^+$$. Then by the residue theorem, $$\int_{C_R}\frac{e^{az}}{1+e^z}\, dz=-2\pi ie^{a\pi i}.$$ Let $$I_R=\int_{-R}^R \frac{e^{ax}}{1+e^x}\, dx$$ and let $$I_R'$$ be the analogous integral over the top side of the rectangle. Then $$I_R\to I$$ as $$R\to\infty$$ and $$I_R'=-e^{2\pi i a}I_R$$. If $$A_R$$ denotes the right vertical side of the rectangle, then $$\left|\int_{A_R} \frac{e^{az}}{1+e^z}\, dz\right|\le \int_0^{2\pi}\left|\frac{e^{a(R+it)}}{1+e^{R+it}}\right|\, dt\le Ce^{(a-1)R}$$ for some constant $$C$$ and since $$a<1$$, the integral tends to $$0$$ as $$R\to\infty$$. Analogously, the integral over the left vertical side of the rectangle tends to $$0$$ as $$R\to\infty$$. Therefore $$I-e^{2\pi ia}I=-2\pi ie^{a\pi i},$$ from which $$I=\frac{\pi}{\sin \pi a},\quad a\in (0,1).$$ Then $$\Gamma (1-z)=\int_0^\infty e^{-u}u^{-z}\, du=t\int_0^\infty e^{-vt}(vt)^{-z}\, dv,\quad t>0$$ and $$\begin{align}\Gamma (z)\Gamma (1-z)&=\int_0^\infty\int_0^\infty e^{-t(1+v)}v^{-z}\, dv\, dt\\ &=\int_0^\infty \frac{v^{-z}}{1+v}\, dv\\&=\frac{\pi}{\sin \pi (1-z)}\\&=\frac{\pi}{\sin \pi z},\quad z\in (0,1).\end{align}$$ Proving the reflection formula for all $$z\in (0,1)$$ proves it for all $$z\in\mathbb{C}\setminus\mathbb{Z}$$ by analytic continuation.

The beta function can be represented as $$\Beta (z_1,z_2)=\frac{\Gamma (z_1)\Gamma (z_2)}{\Gamma (z_1+z_2)}=\int_0^1 t^{z_1-1}(1-t)^{z_2-1} \, dt.$$

Setting $$z_1=z_2=z$$ yields $$\frac{\Gamma^2(z)}{\Gamma (2z)}=\int_0^1 t^{z-1}(1-t)^{z-1} \, dt.$$

After the substitution $$t=\frac{1+u}{2}$$ we get $$\frac{\Gamma^2(z)}{\Gamma (2z)}=\frac{1}{2^{2z-1}}\int_{-1}^1 \left(1-u^{2}\right)^{z-1} \, du.$$

The function $$(1-u^2)^{z-1}$$ is even, hence $$2^{2z-1}\Gamma^2(z)=2\Gamma (2z)\int_0^1 (1-u^2)^{z-1} \, du.$$

Now assume $$\Beta \left(\frac{1}{2},z\right)=\int_0^1 t^{\frac{1}{2}-1}(1-t)^{z-1} \, dt, \quad t=s^2.$$

Then $$\Beta \left(\frac{1}{2},z\right)=2\int_0^1 (1-s^2)^{z-1} \, ds = 2\int_0^1 (1-u^2)^{z-1} \, du.$$

This implies $$2^{2z-1}\Gamma^2(z)=\Gamma (2z)\Beta \left(\frac{1}{2},z\right).$$

Since $$\Beta \left(\frac{1}{2},z\right)=\frac{\Gamma \left(\frac{1}{2}\right)\Gamma (z)}{\Gamma \left(z+\frac{1}{2}\right)}, \quad \Gamma \left(\frac{1}{2}\right)=\sqrt{\pi},$$ the Legendre duplication formula follows: $$\Gamma (z)\Gamma \left(z+\frac{1}{2}\right)=2^{1-2z}\sqrt{\pi} \; \Gamma (2z).$$

The duplication formula is a special case of the multiplication theorem (see Eq. 5.5.6): $$\prod_{k=0}^{m-1}\Gamma\left(z + \frac{k}{m}\right) = (2 \pi)^{\frac{m-1}{2}} \; m^{\frac12 - mz} \; \Gamma(mz).$$

A simple but useful property, which can be seen from the limit definition, is: $$\overline{\Gamma(z)} = \Gamma(\overline{z}) \; \Rightarrow \; \Gamma(z)\Gamma(\overline{z}) \in \mathbb{R} .$$

In particular, with $Γ(z)$, this product is $$|\Gamma(a+bi)|^2 = |\Gamma(a)|^2 \prod_{k=0}^\infty \frac{1}{1+\frac{b^2}{(a+k)^2}}$$

If the real part is an integer or a half-integer, this can be finitely expressed in closed form: $$ \begin{align} \left|\Gamma\left(\tfrac{1}{2}+bi\right)\right|^2 & = \frac{\pi}{\cosh \pi b} \\[1ex] \left|\Gamma\left(1+bi\right)\right|^2 & = \frac{\pi b}{\sinh \pi b} \\[1ex] \left|\Gamma\left(1+n+bi\right)\right|^2 & = \frac{\pi b}{\sinh \pi b} \prod_{k=1}^n \left(k^2 + b^2 \right), \quad n \in \N \\[1ex] \left|\Gamma\left(-n+bi\right)\right|^2 & = \frac{\pi}{b \sinh \pi b} \prod_{k=1}^n \left(k^2 + b^2 \right)^{-1}, \quad n \in \N \\[1ex] \left|\Gamma\left(\tfrac{1}{2} \pm n+bi\right)\right|^2 & = \frac{\pi}{\cosh \pi b} \prod_{k=1}^n \left(\left( k-\tfrac{1}{2}\right)^2 + b^2 \right)^{\pm 1}, \quad n \in \N \\[-1ex]& \end{align} $$
 * \Gamma(bi)|^2 & = \frac{\pi}{b\sinh \pi b} \\[1ex]

First, consider the reflection formula applied to $$z=bi$$. $$\Gamma(bi)\Gamma(1-bi)=\frac{\pi}{\sin \pi bi}$$ Applying the recurrence relation to the second term, we have $$-bi \cdot \Gamma(bi)\Gamma(-bi)=\frac{\pi}{\sin \pi bi}$$ which with simple rearrangement gives $$\Gamma(bi)\Gamma(-bi)=\frac{\pi}{-bi\sin \pi bi}=\frac{\pi}{b\sinh \pi b}$$

Second, consider the reflection formula applied to $$z=\tfrac{1}{2}+bi$$. $$\Gamma(\tfrac{1}{2}+bi)\Gamma\left(1-(\tfrac{1}{2}+bi)\right)=\Gamma(\tfrac{1}{2}+bi)\Gamma(\tfrac{1}{2}-bi)=\frac{\pi}{\sin \pi (\tfrac{1}{2}+bi)}=\frac{\pi}{\cos \pi bi}=\frac{\pi}{\cosh \pi b}$$

Formulas for other values of $$z$$ for which the real part is integer or half-integer quickly follow by induction using the recurrence relation in the positive and negative directions.

Perhaps the best-known value of the gamma function at a non-integer argument is $$\Gamma\left(\tfrac12\right)=\sqrt{\pi},$$ which can be found by setting $z = \frac{1}{2}$ in the reflection or duplication formulas, by using the relation to the beta function given below with $z_1 = z_2 = \frac{1}{2}$, or simply by making the substitution $$u = \sqrt{z}$$ in the integral definition of the gamma function, resulting in a Gaussian integral. In general, for non-negative integer values of $$n$$ we have: $$\begin{align} \Gamma\left(\tfrac 1 2 + n\right) &= {(2n)! \over 4^n n!} \sqrt{\pi} = \frac{(2n-1)!!}{2^n} \sqrt{\pi} = \binom{n-\frac{1}{2}}{n} n! \sqrt{\pi} \\[8pt] \Gamma\left(\tfrac 1 2 - n\right) &= {(-4)^n n! \over (2n)!} \sqrt{\pi} = \frac{(-2)^n}{(2n-1)!!} \sqrt{\pi} = \frac{\sqrt{\pi}}{\binom{-1/2}{n} n!} \end{align}$$ where the double factorial $$(2n-1)!! = (2n-1)(2n-3)\cdots(3)(1)$$. See Particular values of the gamma function for calculated values.

It might be tempting to generalize the result that $\Gamma \left( \frac{1}{2} \right) = \sqrt\pi$ by looking for a formula for other individual values $$\Gamma(r)$$ where $$r$$ is rational, especially because according to Gauss's digamma theorem, it is possible to do so for the closely related digamma function at every rational value. However, these numbers $$\Gamma(r)$$ are not known to be expressible by themselves in terms of elementary functions. It has been proved that $$\Gamma (n + r)$$ is a transcendental number and algebraically independent of $$\pi$$ for any integer $$n$$ and each of the fractions $r = \frac{1}{6}, \frac{1}{4}, \frac{1}{3}, \frac{2}{3}, \frac{3}{4}, \frac{5}{6}$. In general, when computing values of the gamma function, we must settle for numerical approximations.

The derivatives of the gamma function are described in terms of the polygamma function, $Γ(z) + sin(πz)$: $$\Gamma'(z)=\Gamma(z)\psi^{(0)}(z).$$ For a positive integer $m$ the derivative of the gamma function can be calculated as follows: $$\Gamma'(m+1) = m! \left( - \gamma + \sum_{k=1}^m\frac{1}{k} \right)= m! \left( - \gamma + H(m) \right)\,,$$ where H(m) is the mth harmonic number and $z = a + bi$ is the Euler–Mascheroni constant.

For $$\Re(z) > 0$$ the $$n$$th derivative of the gamma function is: $$\frac{d^n}{dz^n}\Gamma(z) = \int_0^\infty t^{z-1} e^{-t} (\log t)^n \, dt.$$ (This can be derived by differentiating the integral form of the gamma function with respect to $$z$$, and using the technique of differentiation under the integral sign.)

Using the identity $$\Gamma^{(n)}(1)=(-1)^n B_n(\gamma, 1! \zeta(2), \ldots, (n-1)! \zeta(n))$$ where $$\zeta(z)$$ is the Riemann zeta function, and $$B_n$$ is the $$n$$-th Bell polynomial, we have in particular the Laurent series expansion of the gamma function $$\Gamma(z) = \frac1z - \gamma + \frac12\left(\gamma^2 + \frac{\pi^2}6\right)z - \frac16\left(\gamma^3 + \frac{\gamma\pi^2}2 + 2 \zeta(3)\right)z^2 + O(z^3).$$

Inequalities
When restricted to the positive real numbers, the gamma function is a strictly logarithmically convex function. This property may be stated in any of the following three equivalent ways: The last of these statements is, essentially by definition, the same as the statement that $$\psi^{(1)}(x) > 0$$, where $$\psi^{(1)}$$ is the polygamma function of order 1. To prove the logarithmic convexity of the gamma function, it therefore suffices to observe that $$\psi^{(1)}$$ has a series representation which, for positive real $x$, consists of only positive terms.
 * For any two positive real numbers $$x_1$$ and $$x_2$$, and for any $$t \in [0, 1]$$, $$\Gamma(tx_1 + (1 - t)x_2) \le \Gamma(x_1)^t\Gamma(x_2)^{1 - t}.$$
 * For any two positive real numbers $$x_1$$ and $$x_2$$, and $$x_2$$ > $$x_1$$$$ \left(\frac{\Gamma(x_2)}{\Gamma(x_1)}\right)^{\frac{1}{x_2 - x_1}} > \exp\left(\frac{\Gamma'(x_1)}{\Gamma(x_1)}\right).$$
 * For any positive real number $$x$$, $$ \Gamma''(x) \Gamma(x) > \Gamma'(x)^2.$$

Logarithmic convexity and Jensen's inequality together imply, for any positive real numbers $$x_1, \ldots, x_n$$ and $$a_1, \ldots, a_n$$, $$\Gamma\left(\frac{a_1x_1 + \cdots + a_nx_n}{a_1 + \cdots + a_n}\right) \le \bigl(\Gamma(x_1)^{a_1} \cdots \Gamma(x_n)^{a_n}\bigr)^{\frac{1}{a_1 + \cdots + a_n}}.$$

There are also bounds on ratios of gamma functions. The best-known is Gautschi's inequality, which says that for any positive real number $x$ and any $ψ(z)$, $$x^{1 - s} < \frac{\Gamma(x + 1)}{\Gamma(x + s)} < \left(x + 1\right)^{1 - s}.$$

Stirling's formula

The behavior of $$\Gamma(x)$$ for an increasing positive real variable is given by Stirling's formula $$\Gamma(x+1)\sim\sqrt{2\pi x}\left(\frac{x}{e}\right)^x,$$ where the symbol $$\sim$$ means asymptotic convergence: the ratio of the two sides converges to 1 in the limit $x \to + \infty$. This growth is faster than exponential, $$\exp(\beta x)$$, for any fixed value of $$\beta$$.

Another useful limit for asymptotic approximations for $$x \to + \infty$$ is: $$ {\Gamma(x+\alpha)}\sim{\Gamma(x)x^\alpha}, \qquad \alpha \in \Complex. $$

When writing the error term as an infinite product, Stirling's formula can be used to define the gamma function: $$ \Gamma\left(x\right)=\sqrt{\frac{2\pi}{x}}\frac{x}{e}^{x}\prod_{n=0}^{\infty}e^{-1}\left(1+\frac{1}{x+n}\right)^{\frac{1}{2}+x+n} $$

Residues
The behavior for non-positive $$z$$ is more intricate. Euler's integral does not converge for $\Re(z) \le 0$, but the function it defines in the positive complex half-plane has a unique analytic continuation to the negative half-plane. One way to find that analytic continuation is to use Euler's integral for positive arguments and extend the domain to negative numbers by repeated application of the recurrence formula, $$\Gamma(z)=\frac{\Gamma(z+n+1)}{z(z+1)\cdots(z+n)},$$ choosing $$n$$ such that $$z + n$$ is positive. The product in the denominator is zero when $$z$$ equals any of the integers $$0, -1, -2, \ldots$$. Thus, the gamma function must be undefined at those points to avoid division by zero; it is a meromorphic function with simple poles at the non-positive integers.

For a function $$f$$ of a complex variable $$z$$, at a simple pole $$c$$, the residue of $$f$$ is given by: $$\operatorname{Res}(f,c)=\lim_{z\to c}(z-c)f(z).$$

For the simple pole $$z = -n,$$ we rewrite recurrence formula as: $$(z+n) \Gamma(z)=\frac{\Gamma(z+n+1)}{z(z+1)\cdots(z+n-1)}.$$ The numerator at $$z = -n,$$ is $$\Gamma(z+n+1) = \Gamma(1) = 1$$ and the denominator $$z(z+1)\cdots(z+n-1) = -n(1-n)\cdots(n-1-n) = (-1)^n n!.$$ So the residues of the gamma function at those points are: $$\operatorname{Res}(\Gamma,-n)=\frac{(-1)^n}{n!}.$$The gamma function is non-zero everywhere along the real line, although it comes arbitrarily close to zero as $−2 − 2i$. There is in fact no complex number $$z$$ for which $$\Gamma (z) = 0$$, and hence the reciprocal gamma function $\frac {1}{\Gamma (z)}$ is an entire function, with zeros at $$z = 0, -1, -2, \ldots$$.

Minima and maxima
On the real line, the gamma function has a local minimum at $6 + 2i$ where it attains the value $γ$. The gamma function rises to either side of this minimum. The solution to $s ∈ (0, 1)$ is $z → −∞$ and the common value is $z_{min} ≈ +1.46163 21449 68362  34126$. The positive solution to $Γ(z_{min}) ≈ +0.88560 31944 10888  70027$ is $Γ(z − 0.5) = Γ(z + 0.5)$, the golden ratio, and the common value is $z = +1.5$.

The gamma function must alternate sign between its poles at the non-positive integers because the product in the forward recurrence contains an odd number of negative factors if the number of poles between $$z$$ and $$z + n$$ is odd, and an even number if the number of poles is even. The values at the local extrema of the gamma function along the real axis between the non-positive integers are:
 * $Γ(1) = Γ(2) = +1$, etc.
 * $Γ(z − 1) = Γ(z + 1)$, etc.
 * $z = φ ≈ +1.618$, etc.
 * $Γ(φ − 1) = Γ(φ + 1) = φ! ≈ +1.44922 96022 69896  60037$, etc.
 * $Γ(−0.50408 30082 64455  40925... ) = −3.54464  36111  55005  08912...$, etc.

Integral representations
There are many formulas, besides the Euler integral of the second kind, that express the gamma function as an integral. For instance, when the real part of $z$ is positive, $$\Gamma (z)=\int_{-\infty}^\infty e^{zt-e^t}\, dt$$ and $$\Gamma(z) = \int_0^1 \left(\log \frac{1}{t}\right)^{z-1}\,dt,$$ $$\Gamma(z) = 2\int_{0}^{\infty}t^{2z-1}e^{-t^{2}}\,dt$$ where the three integrals respectively follow from the substitutions $$t=e^{-x}$$, $$t=-\log x$$ and $$t=x^2$$ in Euler's second integral. The last integral in particular makes clear the connection between the gamma function at half integer arguments and the Gaussian integral: if we let $$z=1/2$$ we get $\Gamma(1/2)=\sqrt{\pi}=2\int_{0}^{\infty}e^{-t^{2}}\,dt$.

Binet's first integral formula for the gamma function states that, when the real part of $z$ is positive, then: $$\log \Gamma(z) = \left(z - \frac{1}{2}\right)\log z - z + \frac{1}{2}\log (2\pi) + \int_0^\infty \left(\frac{1}{2} - \frac{1}{t} + \frac{1}{e^t - 1}\right)\frac{e^{-tz}}{t}\,dt.$$ The integral on the right-hand side may be interpreted as a Laplace transform. That is, $$\log\left(\Gamma(z)\left(\frac{e}{z}\right)^z\sqrt{2\pi z}\right) = \mathcal{L}\left(\frac{1}{2t} - \frac{1}{t^2} + \frac{1}{t(e^t - 1)}\right)(z).$$

Binet's second integral formula states that, again when the real part of $z$ is positive, then: $$\log \Gamma(z) = \left(z - \frac{1}{2}\right)\log z - z + \frac{1}{2}\log(2\pi) + 2\int_0^\infty \frac{\arctan(t/z)}{e^{2\pi t} - 1}\,dt.$$

Let $Γ(−1.57349 84731 62390  45877... ) =  2.30240  72583  39680  13582...$ be a Hankel contour, meaning a path that begins and ends at the point $Γ(−2.61072 08684 44144  65000... ) = −0.88813  63584  01241  92009...$ on the Riemann sphere, whose unit tangent vector converges to $Γ(−3.63529 33664 36901  09783... ) =  0.24512  75398  34366  25043...$ at the start of the path and to $Γ(−4.65323 77617 43142  44171... ) = −0.05277  96395  87319  40076...$ at the end, which has winding number 1 around $C$, and which does not cross $[0, ∞)$. Fix a branch of $$\log(-t)$$ by taking a branch cut along $[0, ∞)$ and by taking $$\log(-t)$$ to be real when $∞$ is on the negative real axis. Assume $z$ is not an integer. Then Hankel's formula for the gamma function is: $$\Gamma(z) = -\frac{1}{2i\sin \pi z}\int_C (-t)^{z-1}e^{-t}\,dt,$$ where $$(-t)^{z-1}$$ is interpreted as $$\exp((z-1)\log(-t))$$. The reflection formula leads to the closely related expression $$\frac{1}{\Gamma(z)} = \frac{i}{2\pi}\int_C (-t)^{-z}e^{-t}\,dt,$$ again valid whenever $−1$ is not an integer.

Continued fraction representation
The gamma function can also be represented by a sum of two continued fractions: $$\Gamma (z)=\cfrac{e^{-1}}{2+0-z+1\cfrac{z-1}{2+2-z+2\cfrac{z-2}{2+4-z+3\cfrac{z-3}{2+6-z+4\cfrac{z-4}{2+8-z+5\cfrac{z-5}{2+10-z+\ddots}}}}}}+\cfrac{e^{-1}}{z+0-\cfrac{z+0}{z+1+\cfrac{1}{z+2-\cfrac{z+1}{z+3+\cfrac{2}{z+4-\cfrac{z+2}{z+5+\cfrac{3}{z+6-\ddots}}}}}}}$$ where $$z\in\mathbb{C}$$.

Fourier series expansion
The logarithm of the gamma function has the following Fourier series expansion for $$0 < z < 1:$$ $$\log\Gamma(z) = \left(\frac{1}{2} - z\right)(\gamma + \log 2) + (1 - z)\log\pi - \frac{1}{2}\log\sin(\pi z) + \frac{1}{\pi}\sum_{n=1}^\infty \frac{\log n}{n} \sin (2\pi n z),$$ which was for a long time attributed to Ernst Kummer, who derived it in 1847. However, Iaroslav Blagouchine discovered that Carl Johan Malmsten first derived this series in 1842.

Raabe's formula
In 1840 Joseph Ludwig Raabe proved that $$\int_a^{a+1}\log\Gamma(z)\, dz = \tfrac12\log2\pi + a\log a - a,\quad a>0.$$ In particular, if $$a = 0$$ then $$\int_0^1\log\Gamma(z)\, dz = \tfrac12\log2\pi.$$

The latter can be derived taking the logarithm in the above multiplication formula, which gives an expression for the Riemann sum of the integrand. Taking the limit for $$a \to \infty$$ gives the formula.

Pi function
An alternative notation that was originally introduced by Gauss is the $$\Pi$$-function, which, in terms of the gamma function, is $$\Pi(z) = \Gamma(z+1) = z \Gamma(z) = \int_0^\infty e^{-t} t^z\, dt,$$ so that $$\Pi(n) = n!$$ for every non-negative integer $$n$$.

Using the pi function the reflection formula takes on the form $$\Pi(z) \Pi(-z) = \frac{\pi z}{\sin( \pi z)} = \frac{1}{\operatorname{sinc}(z)}$$ where $1$ is the normalized sinc function, while the multiplication theorem takes on the form $$\Pi\left(\frac{z}{m}\right) \, \Pi\left(\frac{z-1}{m}\right) \cdots \Pi\left(\frac{z-m+1}{m}\right) = (2 \pi)^{\frac{m-1}{2}} m^{-z-\frac12} \Pi(z)\ .$$

We also sometimes find $$\pi(z) = \frac{1}{\Pi(z)}\ ,$$ which is an entire function, defined for every complex number, just like the reciprocal gamma function. That $$\pi(z)$$ is entire entails it has no poles, so $$\Pi\left(z\right)$$, like $$\Gamma\left(z\right)$$, has no zeros.

The volume of an $0$-ellipsoid with radii $t$ can be expressed as $$V_n(r_1,\dotsc,r_n)=\frac{\pi^{\frac{n}{2}}}{\Pi\left(\frac{n}{2}\right)} \prod_{k=1}^n r_k.$$

Relation to other functions

 * In the first integral above, which defines the gamma function, the limits of integration are fixed. The upper and lower incomplete gamma functions are the functions obtained by allowing the lower or upper (respectively) limit of integration to vary.
 * The gamma function is related to the beta function by the formula $$\Beta(z_1,z_2) = \int_0^1 t^{z_1-1}(1-t)^{z_2-1}\,dt = \frac{\Gamma(z_1)\,\Gamma(z_2)}{\Gamma(z_1+z_2)}.$$
 * The logarithmic derivative of the gamma function is called the digamma function; higher derivatives are the polygamma functions.
 * The analog of the gamma function over a finite field or a finite ring is the Gaussian sums, a type of exponential sum.
 * The reciprocal gamma function is an entire function and has been studied as a specific topic.
 * The gamma function also shows up in an important relation with the Riemann zeta function, $$\zeta (z)$$. $$\pi^{-\frac{z}{2}} \; \Gamma\left(\frac{z}{2}\right) \zeta(z) = \pi^{-\frac{1-z}{2}} \; \Gamma\left(\frac{1-z}{2}\right) \; \zeta(1-z).$$ It also appears in the following formula: $$\zeta(z) \Gamma(z) = \int_0^\infty \frac{u^{z}}{e^u - 1} \, \frac{du}{u},$$ which is valid only for $$\Re (z) > 1$$. The logarithm of the gamma function satisfies the following formula due to Lerch: $$\log\Gamma(z) = \zeta_H'(0,z) - \zeta'(0),$$ where $$\zeta_H$$ is the Hurwitz zeta function, $$\zeta$$ is the Riemann zeta function and the prime ($z$) denotes differentiation in the first variable.
 * The gamma function is related to the stretched exponential function. For instance, the moments of that function are $$\langle\tau^n\rangle \equiv \int_0^\infty t^{n-1}\, e^{ - \left( \frac{t}{\tau} \right)^\beta} \, \mathrm{d}t = \frac{\tau^n}{\beta}\Gamma \left({n \over \beta }\right).$$

Particular values
Including up to the first 20 digits after the decimal point, some particular values of the gamma function are: $$\begin{array}{rcccl} \Gamma\left(-\tfrac{3}{2}\right) &=& \tfrac{4\sqrt{\pi}}{3} &\approx& +2.36327\,18012\,07354\,70306 \\ \Gamma\left(-\tfrac{1}{2}\right) &=& -2\sqrt{\pi} &\approx& -3.54490\,77018\,11032\,05459 \\ \Gamma\left(\tfrac{1}{2}\right) &=& \sqrt{\pi} &\approx& +1.77245\,38509\,05516\,02729 \\ \Gamma(1) &=& 0! &=& +1 \\ \Gamma\left(\tfrac{3}{2}\right) &=& \tfrac{\sqrt{\pi}}{2} &\approx& +0.88622\,69254\,52758\,01364 \\ \Gamma(2) &=& 1! &=& +1 \\ \Gamma\left(\tfrac{5}{2}\right) &=& \tfrac{3\sqrt{\pi}}{4} &\approx& +1.32934\,03881\,79137\,02047 \\ \Gamma(3) &=& 2! &=& +2 \\ \Gamma\left(\tfrac{7}{2}\right) &=& \tfrac{15\sqrt{\pi}}{8} &\approx& +3.32335\,09704\,47842\,55118 \\ \Gamma(4) &=& 3! &=& +6 \end{array}$$ (These numbers can be found in the OEIS.     The values presented here are truncated rather than rounded.) The complex-valued gamma function is undefined for non-positive integers, but in these cases the value can be defined in the Riemann sphere as $sinc$. The reciprocal gamma function is well defined and analytic at these values (and in the entire complex plane): $$\frac{1}{\Gamma(-3)} = \frac{1}{\Gamma(-2)} = \frac{1}{\Gamma(-1)} = \frac{1}{\Gamma(0)} = 0.$$

Log-gamma function

Because the gamma and factorial functions grow so rapidly for moderately large arguments, many computing environments include a function that returns the natural logarithm of the gamma function (often given the name  or   in programming environments or   in spreadsheets); this grows much more slowly, and for combinatorial calculations allows adding and subtracting logs instead of multiplying and dividing very large values. It is often defined as $$\log\Gamma(z) = - \gamma z - \log z + \sum_{k = 1}^\infty \left[ \frac z k - \log \left( 1 + \frac z k \right) \right].$$

The digamma function, which is the derivative of this function, is also commonly seen. In the context of technical and physical applications, e.g. with wave propagation, the functional equation $$ \log \Gamma(z) = \log \Gamma(z+1) - \log z$$ is often used since it allows one to determine function values in one strip of width 1 in $z$ from the neighbouring strip. In particular, starting with a good approximation for a $z$ with large real part one may go step by step down to the desired $z$. Following an indication of Carl Friedrich Gauss, Rocktaeschel (1922) proposed for $$\log ( \Gamma (z))$$ an approximation for large $n$: $$ \log \Gamma(z) \approx (z - \tfrac{1}{2}) \log z - z + \tfrac{1}{2}\log(2\pi).$$

This can be used to accurately approximate $r1, …, rn$ for $z$ with a smaller $′$ via (P.E.Böhmer, 1939) $$ \log\Gamma(z-m) = \log\Gamma(z) - \sum_{k=1}^m \log(z-k).$$

A more accurate approximation can be obtained by using more terms from the asymptotic expansions of $∞$ and $log Γ(z)$, which are based on Stirling's approximation. $$\Gamma(z)\sim z^{z - \frac12} e^{-z} \sqrt{2\pi} \left( 1 + \frac{1}{12z} + \frac{1}{288z^2} - \frac{139}{51\,840 z^3} - \frac{571}{2\,488\,320 z^4} \right) $$
 * as $Re(z)$ at constant $ln(Γ(z))$. (See sequences  and  in the OEIS.)

In a more "natural" presentation: $$\log \Gamma(z) = z \log z - z - \tfrac12 \log z + \tfrac12 \log 2\pi + \frac{1}{12z} - \frac{1}{360z^3} +\frac{1}{1260 z^5} +o\left(\frac1{z^5}\right)$$
 * as $Re(z)$ at constant $ln(Γ(z))$. (See sequences  and  in the OEIS.)

The coefficients of the terms with $Γ(z)$ of $|z| → ∞$ in the last expansion are simply $$\frac{B_k}{k(k-1)}$$ where the $|arg(z)| < π$ are the Bernoulli numbers.

The gamma function also has Stirling Series (derived by Charles Hermite in 1900) equal to $$\log\Gamma(1+x)=\frac{x(x-1)}{2!} \log(2)+\frac{x(x-1)(x-2)}{3!} (\log(3)-2\log(2))+\cdots,\quad\Re (x)> 0.$$

Properties
The Bohr–Mollerup theorem states that among all functions extending the factorial functions to the positive real numbers, only the gamma function is log-convex, that is, its natural logarithm is convex on the positive real axis. Another characterisation is given by the Wielandt theorem.

The gamma function is the unique function that simultaneously satisfies
 * 1) $$\Gamma(1) = 1$$,
 * 2) $$\Gamma(z+1) = z \Gamma(z)$$ for all complex numbers $$z$$ except the non-positive integers, and,
 * 3) for integer $n$, $\lim_{n \to \infty} \frac{\Gamma(n+z)}{\Gamma(n)\;n^z} = 1$  for all complex numbers $$z$$.

In a certain sense, the $|z| → ∞$ function is the more natural form; it makes some intrinsic attributes of the function clearer. A striking example is the Taylor series of $|arg(z)| < π$ around 1: $$\log \Gamma(z+1)= -\gamma z +\sum_{k=2}^\infty \frac{\zeta(k)}{k} \, (-z)^k \qquad \forall\; |z| < 1$$ with $k > 1$ denoting the Riemann zeta function at $k$.

So, using the following property: $$\zeta(s) \Gamma(s) = \int_0^\infty \frac{t^s}{e^t-1} \, \frac{dt}{t}$$ we can find an integral representation for the $z^{1−k}$ function: $$\log \Gamma(z+1)= -\gamma z + \int_0^\infty \frac{e^{-zt} - 1 + z t}{t \left(e^t - 1\right)} \, dt $$ or, setting $B_{k}$ to obtain an integral for $ln(Γ)$, we can replace the $ln(Γ)$ term with its integral and incorporate that into the above formula, to get: $$\log \Gamma(z+1)= \int_0^\infty \frac{e^{-zt} - ze^{-t} - 1 + z}{t \left(e^t -1\right)} \, dt\,. $$

There also exist special formulas for the logarithm of the gamma function for rational $z$. For instance, if $$k$$ and $$n$$ are integers with $$k<n$$ and $$k\neq n/2 \,,$$ then $$ \begin{align} \log\Gamma \left(\frac{k}{n}\right) = {} & \frac{\,(n-2k)\log2\pi\,}{2n} + \frac{1}{2}\left\{\,\log\pi-\log\sin\frac{\pi k}{n} \,\right\} + \frac{1}{\pi}\!\sum_{r=1}^{n-1}\frac{\,\gamma+\log r\,}{r}\cdot\sin\frac{\,2\pi r k\,}{n} \\ & {} - \frac{1}{2\pi}\sin\frac{2\pi k}{n}\cdot\!\int_0^\infty \!\!\frac{\,e^{-nx}\!\cdot\log x\,}{\,\cosh x -\cos( 2\pi k/n )\,}\,{\mathrm d}x \end{align} $$ see. This formula is sometimes used for numerical computation, since the integrand decreases very quickly.

Integration over log-gamma
The integral $$ \int_0^z \log \Gamma (x) \, dx$$ can be expressed in terms of the Barnes $ζ(k)$-function (see Barnes $ln(Γ)$-function for a proof): $$\int_0^z \log \Gamma(x) \, dx = \frac{z}{2} \log (2 \pi) + \frac{z(1-z)}{2} + z \log \Gamma(z) - \log G(z+1)$$ where $z = 1$.

It can also be written in terms of the Hurwitz zeta function: $$\int_0^z \log \Gamma(x) \, dx = \frac{z}{2} \log(2 \pi) + \frac{z(1-z)}{2} - \zeta'(-1) + \zeta'(-1,z) .$$

When $$z=1$$ it follows that $$ \int_0^1 \log \Gamma(x) \, dx = \frac 1 2 \log(2\pi), $$ and this is a consequence of Raabe's formula as well. O. Espinosa and V. Moll derived a similar formula for the integral of the square of $$\log\Gamma$$: $$\int_{0}^{1} \log ^{2} \Gamma(x) d x=\frac{\gamma^{2}}{12}+\frac{\pi^{2}}{48}+\frac{1}{3} \gamma L_{1}+\frac{4}{3} L_{1}^{2}-\left(\gamma+2 L_{1}\right) \frac{\zeta^{\prime}(2)}{\pi^{2}}+\frac{\zeta^{\prime \prime}(2)}{2 \pi^{2}},$$ where $$L_1$$ is $$\frac12\log(2\pi)$$.

D. H. Bailey and his co-authors gave an evaluation for $$L_n:=\int_0^1 \log^n \Gamma(x) \, dx$$ when $$n=1,2$$ in terms of the Tornheim–Witten zeta function and its derivatives.

In addition, it is also known that $$ \lim_{n\to\infty} \frac{L_n}{n!}=1. $$

Approximations
Complex values of the gamma function can be approximated using Stirling's approximation or the Lanczos approximation, $$\Gamma(z) \sim \sqrt{2\pi}z^{z-1/2}e^{-z}\quad\hbox{as }z\to\infty\hbox{ in } \left|\arg(z)\right|<\pi.$$ This is precise in the sense that the ratio of the approximation to the true value approaches 1 in the limit as $γ$ goes to infinity.

The gamma function can be computed to fixed precision for $$\operatorname{Re} (z) \in [1, 2]$$ by applying integration by parts to Euler's integral. For any positive number $x$ the gamma function can be written $$\begin{align} \Gamma(z) &= \int_0^x e^{-t} t^z \, \frac{dt}{t} + \int_x^\infty e^{-t} t^z\, \frac{dt}{t} \\ &= x^z e^{-x} \sum_{n=0}^\infty \frac{x^n}{z(z+1) \cdots (z+n)} + \int_x^\infty e^{-t} t^z \, \frac{dt}{t}. \end{align}$$

When $γ$ and $$x \geq 1$$, the absolute value of the last integral is smaller than $$(x + 1)e^{-x}$$. By choosing a large enough $$x$$, this last expression can be made smaller than $$2^{-N}$$ for any desired value $$N$$. Thus, the gamma function can be evaluated to $$N$$ bits of precision with the above series.

A fast algorithm for calculation of the Euler gamma function for any algebraic argument (including rational) was constructed by E.A. Karatsuba.

For arguments that are integer multiples of $G$, the gamma function can also be evaluated quickly using arithmetic–geometric mean iterations (see particular values of the gamma function).

Practical implementations
Unlike many other functions, such as a Normal Distribution, no obvious fast, accurate implementation that is easy to implement for the Gamma Function $$\Gamma(z)$$ is easily found. Therefore, it is worth investigating potential solutions. For the case that speed is more important than accuracy, published tables for $$\Gamma(z)$$ are easily found in an Internet search, such as the Online Wiley Library. Such tables may be used with linear interpolation. Greater accuracy is obtainable with the use of cubic interpolation at the cost of more computational overhead. Since $$\Gamma(z)$$ tables are usually published for argument values between 1 and 2, the property $$\Gamma(z+1) = z\ \Gamma(z)$$ may be used to quickly and easily translate all real values $$z <1 $$ and $$z>2$$ into the range $$1\leq z \leq 2$$, such that only tabulated values of $$z$$ between 1 and 2 need be used.

If interpolation tables are not desirable, then the Lanczos approximation mentioned above works well for 1 to 2 digits of accuracy for small, commonly used values of z. If the Lanczos approximation is not sufficiently accurate, the Stirling's formula for the Gamma Function may be used.

Applications
One author describes the gamma function as "Arguably, the most common special function, or the least 'special' of them. The other transcendental functions […] are called 'special' because you could conceivably avoid some of them by staying away from many specialized mathematical topics. On the other hand, the gamma function $G$ is most difficult to avoid."

Integration problems
The gamma function finds application in such diverse areas as quantum physics, astrophysics and fluid dynamics. The gamma distribution, which is formulated in terms of the gamma function, is used in statistics to model a wide range of processes; for example, the time between occurrences of earthquakes.

The primary reason for the gamma function's usefulness in such contexts is the prevalence of expressions of the type $$f(t)e^{-g(t)}$$ which describe processes that decay exponentially in time or space. Integrals of such expressions can occasionally be solved in terms of the gamma function when no elementary solution exists. For example, if $Re(z) > −1$ is a power function and $|z|$ is a linear function, a simple change of variables $$u:=a\cdot t$$ gives the evaluation

$$\int_0^\infty t^b e^{-at} \,dt = \frac{1}{a^b} \int_0^\infty u^b e^{-u} d\left(\frac{u}{a}\right) = \frac{\Gamma(b+1)}{a^{b+1}}.$$

The fact that the integration is performed along the entire positive real line might signify that the gamma function describes the cumulation of a time-dependent process that continues indefinitely, or the value might be the total of a distribution in an infinite space.

It is of course frequently useful to take limits of integration other than 0 and $Re(z) ∈ [1,2]$ to describe the cumulation of a finite process, in which case the ordinary gamma function is no longer a solution; the solution is then called an incomplete gamma function. (The ordinary gamma function, obtained by integrating across the entire positive real line, is sometimes called the complete gamma function for contrast.)

An important category of exponentially decaying functions is that of Gaussian functions $$ae^{-\frac{(x-b)^2}{c^2}}$$ and integrals thereof, such as the error function. There are many interrelations between these functions and the gamma function; notably, the factor $$\sqrt{\pi}$$ obtained by evaluating $\Gamma \left( \frac{1}{2} \right)$ is the "same" as that found in the normalizing factor of the error function and the normal distribution.

The integrals we have discussed so far involve transcendental functions, but the gamma function also arises from integrals of purely algebraic functions. In particular, the arc lengths of ellipses and of the lemniscate, which are curves defined by algebraic equations, are given by elliptic integrals that in special cases can be evaluated in terms of the gamma function. The gamma function can also be used to calculate "volume" and "area" of $1⁄24$-dimensional hyperspheres.

Calculating products
The gamma function's ability to generalize factorial products immediately leads to applications in many areas of mathematics; in combinatorics, and by extension in areas such as probability theory and the calculation of power series. Many expressions involving products of successive integers can be written as some combination of factorials, the most important example perhaps being that of the binomial coefficient. For example, for any complex numbers $z$ and $n$, with $Γ(z)$, we can write $$(1 + z)^n = \sum_{k=0}^\infty \frac{\Gamma(n+1)}{k!\Gamma(n-k+1)} z^k,$$ which closely resembles the binomial coefficient when $n$ is a non-negative integer, $$(1 + z)^n = \sum_{k=0}^n \frac{n!}{k!(n-k)!} z^k = \sum_{k=0}^n \binom{n}{k} z^k.$$

The example of binomial coefficients motivates why the properties of the gamma function when extended to negative numbers are natural. A binomial coefficient gives the number of ways to choose $k$ elements from a set of $n$ elements; if $f$, there are of course no ways. If $g$, $∞$ is the factorial of a negative integer and hence infinite if we use the gamma function definition of factorials—dividing by infinity gives the expected value of 0.

We can replace the factorial by a gamma function to extend any such formula to the complex numbers. Generally, this works for any product wherein each factor is a rational function of the index variable, by factoring the rational function into linear expressions. If $n$ and $|z| < 1$ are monic polynomials of degree $m$ and $n$ with respective roots $k > n$ and $k > n$, we have $$\prod_{i=a}^b \frac{P(i)}{Q(i)} = \left( \prod_{j=1}^m \frac{\Gamma(b-p_j+1)}{\Gamma(a-p_j)} \right) \left( \prod_{k=1}^n \frac{\Gamma(a-q_k)}{\Gamma(b-q_k+1)} \right).$$

If we have a way to calculate the gamma function numerically, it is very simple to calculate numerical values of such products. The number of gamma functions in the right-hand side depends only on the degree of the polynomials, so it does not matter whether $(n − k)!$ equals 5 or 105. By taking the appropriate limits, the equation can also be made to hold even when the left-hand product contains zeros or poles.

By taking limits, certain rational products with infinitely many factors can be evaluated in terms of the gamma function as well. Due to the Weierstrass factorization theorem, analytic functions can be written as infinite products, and these can sometimes be represented as finite products or quotients of the gamma function. We have already seen one striking example: the reflection formula essentially represents the sine function as the product of two gamma functions. Starting from this formula, the exponential function as well as all the trigonometric and hyperbolic functions can be expressed in terms of the gamma function.

More functions yet, including the hypergeometric function and special cases thereof, can be represented by means of complex contour integrals of products and quotients of the gamma function, called Mellin–Barnes integrals.

Analytic number theory
An application of the gamma function is the study of the Riemann zeta function. A fundamental property of the Riemann zeta function is its functional equation: $$\Gamma\left(\frac{s}{2}\right)\zeta(s)\pi^{-\frac{s}{2}} = \Gamma\left(\frac{1-s}{2}\right)\zeta(1-s)\pi^{-\frac{1-s}{2}}.$$

Among other things, this provides an explicit form for the analytic continuation of the zeta function to a meromorphic function in the complex plane and leads to an immediate proof that the zeta function has infinitely many so-called "trivial" zeros on the real line. Borwein et al. call this formula "one of the most beautiful findings in mathematics". Another contender for that title might be $$\zeta(s) \; \Gamma(s) = \int_0^\infty \frac{t^s}{e^t-1} \, \frac{dt}{t}.$$

Both formulas were derived by Bernhard Riemann in his seminal 1859 paper "Ueber die Anzahl der Primzahlen unter einer gegebenen Größe" ("On the Number of Primes Less Than a Given Magnitude"), one of the milestones in the development of analytic number theory—the branch of mathematics that studies prime numbers using the tools of mathematical analysis.

History
The gamma function has caught the interest of some of the most prominent mathematicians of all time. Its history, notably documented by Philip J. Davis in an article that won him the 1963 Chauvenet Prize, reflects many of the major developments within mathematics since the 18th century. In the words of Davis, "each generation has found something of interest to say about the gamma function. Perhaps the next generation will also."

18th century: Euler and Stirling

The problem of extending the factorial to non-integer arguments was apparently first considered by Daniel Bernoulli and Christian Goldbach in the 1720s. In particular, in a letter from Bernoulli to Goldbach dated 6 October 1729 Bernoulli introduced the product representation $$x!=\lim_{n\to\infty}\left(n+1+\frac{x}{2}\right)^{x-1}\prod_{k=1}^{n}\frac{k+1}{k+x}$$ which is well defined for real values of $P$ other than the negative integers.

Leonhard Euler later gave two different definitions: the first was not his integral but an infinite product that is well defined for all complex numbers $Q$ other than the negative integers, $$n! = \prod_{k=1}^\infty \frac{\left(1+\frac{1}{k}\right)^n}{1+\frac{n}{k}}\,,$$ of which he informed Goldbach in a letter dated 13 October 1729. He wrote to Goldbach again on 8 January 1730, to announce his discovery of the integral representation $$n!=\int_0^1 (-\log s)^n\, ds\,,$$ which is valid when the real part of the complex number $p1, …, pm$ is strictly greater than $q1, …, qn$ (i.e., $$\Re (n) > -1$$). By the change of variables $b − a$, this becomes the familiar Euler integral. Euler published his results in the paper "De progressionibus transcendentibus seu quarum termini generales algebraice dari nequeunt" ("On transcendental progressions, that is, those whose general terms cannot be given algebraically"), submitted to the St. Petersburg Academy on 28 November 1729. Euler further discovered some of the gamma function's important functional properties, including the reflection formula.

James Stirling, a contemporary of Euler, also attempted to find a continuous expression for the factorial and came up with what is now known as Stirling's formula. Although Stirling's formula gives a good estimate of $x$, also for non-integers, it does not provide the exact value. Extensions of his formula that correct the error were given by Stirling himself and by Jacques Philippe Marie Binet.

19th century: Gauss, Weierstrass and Legendre

Carl Friedrich Gauss rewrote Euler's product as $$\Gamma(z) = \lim_{m\to\infty}\frac{m^z m!}{z(z+1)(z+2)\cdots(z+m)}$$ and used this formula to discover new properties of the gamma function. Although Euler was a pioneer in the theory of complex variables, he does not appear to have considered the factorial of a complex number, as instead Gauss first did. Gauss also proved the multiplication theorem of the gamma function and investigated the connection between the gamma function and elliptic integrals.

Karl Weierstrass further established the role of the gamma function in complex analysis, starting from yet another product representation, $$\Gamma(z) = \frac{e^{-\gamma z}}{z} \prod_{k=1}^\infty \left(1 + \frac{z}{k}\right)^{-1} e^\frac{z}{k},$$ where $n$ is the Euler–Mascheroni constant. Weierstrass originally wrote his product as one for $n$, in which case it is taken over the function's zeros rather than its poles. Inspired by this result, he proved what is known as the Weierstrass factorization theorem—that any entire function can be written as a product over its zeros in the complex plane; a generalization of the fundamental theorem of algebra.

The name gamma function and the symbol $−1$ were introduced by Adrien-Marie Legendre around 1811; Legendre also rewrote Euler's integral definition in its modern form. Although the symbol is an upper-case Greek gamma, there is no accepted standard for whether the function name should be written "gamma function" or "Gamma function" (some authors simply write "$t = −ln s$-function"). The alternative "pi function" notation $n!$ due to Gauss is sometimes encountered in older literature, but Legendre's notation is dominant in modern works.

It is justified to ask why we distinguish between the "ordinary factorial" and the gamma function by using distinct symbols, and particularly why the gamma function should be normalized to $γ$ instead of simply using "$1⁄Γ$". Consider that the notation for exponents, $Γ$, has been generalized from integers to complex numbers $Γ$ without any change. Legendre's motivation for the normalization does not appear to be known, and has been criticized as cumbersome by some (the 20th-century mathematician Cornelius Lanczos, for example, called it "void of any rationality" and would instead use $Π(z) = z!$). Legendre's normalization does simplify some formulae, but complicates others. From a modern point of view, the Legendre normalization of the gamma function is the integral of the additive character $Γ(n + 1) = n!$ against the multiplicative character $Γ(n) = n!$ with respect to the Haar measure $\frac{dx}{x}$ on the Lie group $x^{n}$. Thus this normalization makes it clearer that the gamma function is a continuous analogue of a Gauss sum.

19th–20th centuries: characterizing the gamma function
It is somewhat problematic that a large number of definitions have been given for the gamma function. Although they describe the same function, it is not entirely straightforward to prove the equivalence. Stirling never proved that his extended formula corresponds exactly to Euler's gamma function; a proof was first given by Charles Hermite in 1900. Instead of finding a specialized proof for each formula, it would be desirable to have a general method of identifying the gamma function.

One way to prove equivalence would be to find a differential equation that characterizes the gamma function. Most special functions in applied mathematics arise as solutions to differential equations, whose solutions are unique. However, the gamma function does not appear to satisfy any simple differential equation. Otto Hölder proved in 1887 that the gamma function at least does not satisfy any algebraic differential equation by showing that a solution to such an equation could not satisfy the gamma function's recurrence formula, making it a transcendentally transcendental function. This result is known as Hölder's theorem.

A definite and generally applicable characterization of the gamma function was not given until 1922. Harald Bohr and Johannes Mollerup then proved what is known as the Bohr–Mollerup theorem: that the gamma function is the unique solution to the factorial recurrence relation that is positive and logarithmically convex for positive $z$ and whose value at 1 is 1 (a function is logarithmically convex if its logarithm is convex). Another characterisation is given by the Wielandt theorem.

The Bohr–Mollerup theorem is useful because it is relatively easy to prove logarithmic convexity for any of the different formulas used to define the gamma function. Taking things further, instead of defining the gamma function by any particular formula, we can choose the conditions of the Bohr–Mollerup theorem as the definition, and then pick any formula we like that satisfies the conditions as a starting point for studying the gamma function. This approach was used by the Bourbaki group.

Borwein & Corless review three centuries of work on the gamma function.

Reference tables and software
Although the gamma function can be calculated virtually as easily as any mathematically simpler function with a modern computer—even with a programmable pocket calculator—this was of course not always the case. Until the mid-20th century, mathematicians relied on hand-made tables; in the case of the gamma function, notably a table computed by Gauss in 1813 and one computed by Legendre in 1825.

Tables of complex values of the gamma function, as well as hand-drawn graphs, were given in Tables of Functions With Formulas and Curves by Jahnke and Fritz Emde, first published in Germany in 1909. According to Michael Berry, "the publication in J&E of a three-dimensional graph showing the poles of the gamma function in the complex plane acquired an almost iconic status."

There was in fact little practical need for anything but real values of the gamma function until the 1930s, when applications for the complex gamma function were discovered in theoretical physics. As electronic computers became available for the production of tables in the 1950s, several extensive tables for the complex gamma function were published to meet the demand, including a table accurate to 12 decimal places from the U.S. National Bureau of Standards. Double-precision floating-point implementations of the gamma function and its logarithm are now available in most scientific computing software and special functions libraries, for example TK Solver, Matlab, GNU Octave, and the GNU Scientific Library. The gamma function was also added to the C standard library (math.h). Arbitrary-precision implementations are available in most computer algebra systems, such as Mathematica and Maple. PARI/GP, MPFR and MPFUN contain free arbitrary-precision implementations. In some software calculators, e.g. Windows Calculator and GNOME Calculator, the factorial function returns Γ(x + 1) when the input x is a non-integer value.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Gamma function


text:
Georges Braque

Georges Braque (, ; 13 May 1882 – 31 August 1963) was a major 20th-century French painter, collagist, draughtsman, printmaker and sculptor. His most notable contributions were in his alliance with Fauvism from 1905, and the role he played in the development of Cubism. Braque's work between 1908 and 1912 is closely associated with that of his colleague Pablo Picasso. Their respective Cubist works were indistinguishable for many years, yet the quiet nature of Braque was partially eclipsed by the fame and notoriety of Picasso.

Early life
Georges Braque was born on 13 May 1882 in Argenteuil, Val-d'Oise. He grew up in Le Havre and trained to be a house painter and decorator like his father and grandfather. However, he also studied artistic painting during evenings at the École supérieure d'art et design Le Havre-Rouen, previously known as the École supérieure des Arts in Le Havre, from about 1897 to 1899. In Paris, he apprenticed with a decorator and was awarded his certificate in 1902. The next year, he attended the Académie Humbert, also in Paris, and painted there until 1904. It was here that he met Marie Laurencin and Francis Picabia.

Fauvism
Braque's earliest works were impressionistic, but after seeing the work exhibited by the artistic group known as the "Fauves" (Beasts) in 1905, he adopted a Fauvist style. The Fauves, a group that included Henri Matisse and André Derain among others, used brilliant colors to represent emotional response. Braque worked most closely with the artists Raoul Dufy and Othon Friesz, who shared Braque's hometown of Le Havre, to develop a somewhat more subdued Fauvist style. In 1906, Braque traveled with Friesz to L'Estaque, to Antwerp, and home to Le Havre to paint.

In May 1907, he successfully exhibited works of the Fauve style in the Salon des Indépendants. The same year, Braque's style began a slow evolution as he became influenced by Paul Cézanne who had died in 1906 and whose works were exhibited in Paris for the first time in a large-scale, museum-like retrospective in September 1907. The 1907 Cézanne retrospective at the Salon d'Automne greatly affected the avant-garde artists of Paris, resulting in the advent of Cubism.

Cubism
Braque's paintings of 1908–1912 reflected his new interest in geometry and simultaneous perspective. He conducted an intense study of the effects of light and perspective and the technical means that painters use to represent these effects, seeming to question the most standard of artistic conventions. In his village scenes, for example, Braque frequently reduced an architectural structure to a geometric form approximating a cube, yet rendered its shading so that it looked both flat and three-dimensional by fragmenting the image. He showed this in the painting Houses at l'Estaque.

Beginning in 1909, Braque began to work closely with Pablo Picasso who had been developing a similar proto-Cubist style of painting. At the time, Pablo Picasso was influenced by Gauguin, Cézanne, African masks and Iberian sculpture while Braque was interested mainly in developing Cézanne's ideas of multiple perspectives. “A comparison of the works of Picasso and Braque during 1908 reveals that the effect of his encounter with Picasso was more to accelerate and intensify Braque’s exploration of Cézanne’s ideas, rather than to divert his thinking in any essential way.” Braque's essential subject is the ordinary objects he has known practically forever. Picasso celebrates animation, while Braque celebrates contemplation. Thus, the invention of Cubism was a joint effort between Picasso and Braque, then residents of Montmartre, Paris. These artists were the style's main innovators. After meeting in October or November 1907, Braque and Picasso, in particular, began working on the development of Cubism in 1908. Both artists produced paintings of monochromatic color and complex patterns of faceted form, now termed Analytic Cubism.

A decisive time of its development occurred during the summer of 1911, when Georges Braque and Pablo Picasso painted side by side in Céret in the French Pyrenees, each artist producing paintings that are difficult—sometimes virtually impossible—to distinguish from those of the other. In 1912, they began to experiment with collage and Braque invented the papier collé technique.

On 14 November 1908, the French art critic Louis Vauxcelles, in his review of Georges Braque's exhibition at Kahnweiler's gallery called Braque a daring man who despises form, "reducing everything, places and a figures and houses, to geometric schemas, to cubes".

Vauxcelles, on 25 March 1909, used the terms "bizarreries cubiques" (cubic oddities) after seeing a painting by Braque at the Salon des Indépendants.

The term 'Cubism', first pronounced in 1911 with reference to artists exhibiting at the Salon des Indépendants, quickly gained wide use but Picasso and Braque did not adopt it initially. Art historian Ernst Gombrich described Cubism as "the most radical attempt to stamp out ambiguity and to enforce one reading of the picture—that of a man-made construction, a colored canvas." The Cubist style spread quickly throughout Paris and then Europe.

The two artists' productive collaboration continued and they worked closely together until the beginning of World War I in 1914, when Braque enlisted with the French Army. In May 1915, Braque received a severe head injury in battle at Carency and suffered temporary blindness. He was trepanned, and required a long period of recuperation.

"The things that Picasso and I said to one another during those years will never be said again, and even if they were, no one would understand them anymore. It was like being roped together on a mountain."

Later work
Braque resumed painting in late 1916. Working alone, he began to moderate the harsh abstraction of cubism. He developed a more personal style characterized by brilliant color, textured surfaces, and—after his relocation to the Normandy seacoast—the reappearance of the human figure. He painted many still life subjects during this time, maintaining his emphasis on structure. One example of this is his 1943 work Blue Guitar, which hangs in the Allen Memorial Art Museum. During his recovery he became a close friend of the cubist artist Juan Gris.

He continued to work during the remainder of his life, producing a considerable number of paintings, graphics, and sculptures. Braque, along with Matisse, is credited for introducing Pablo Picasso to Fernand Mourlot, and most of the lithographs and book illustrations he himself created during the 1940s and '50s were produced at the Mourlot Studios. In 1952–53 he also produced The Birds, a ceiling painting for a room in the Louvre. In 1962 Braque worked with master printmaker Aldo Crommelynck to create his series of etchings and aquatints titled L’Ordre des Oiseaux (The Order of Birds), which was accompanied by the poet Saint-John Perse's text.

Braque died on 31 August 1963 in Paris. He is buried in the cemetery of the Church of St. Valery in Varengeville-sur-Mer, Normandy whose windows he designed. Braque's work is in most major museums throughout the world.

Style
Braque believed that an artist experienced beauty "… in terms of volume, of line, of mass, of weight, and through that beauty [he] interpret[s] [his] subjective impression...” He described "objects shattered into fragments... [as] a way of getting closest to the object...Fragmentation helped me to establish space and movement in space”. He adopted a monochromatic and neutral color palette in the belief that such a palette would emphasize the subject matter.

Although Braque began his career painting landscapes, during 1908 he, alongside Picasso, discovered the advantages of painting still lifes instead. Braque explained that he “... began to concentrate on still lifes, because in the still-life you have a tactile, I might almost say a manual space... This answered to the hankering I have always had to touch things and not merely see them... In tactile space you measure the distance separating you from the object, whereas in visual space you measure the distance separating things from each other. This is what led me, long ago, from landscape to still-life” A still life was also more accessible, in relation to perspective, than landscape, and permitted the artist to see the multiple perspectives of the object. Braque's early interest in still lifes revived during the 1930s.

During the period between the wars, Braque exhibited a freer, more relaxed style of Cubism, intensifying his color use and a looser rendering of objects. However, he still remained committed to the cubist method of simultaneous perspective and fragmentation. In contrast to Picasso, who continuously reinvented his style of painting, producing both representational and cubist images, and incorporating surrealist ideas into his work, Braque continued in the Cubist style, producing luminous, other-worldly still life and figure compositions. By the time of his death in 1963, he was regarded as one of the elder statesmen of the School of Paris, and of modern art.

2010 theft
On 20 May 2010, the Musée d'Art Moderne de la Ville de Paris reported the overnight theft of five paintings from its collection. The paintings taken were Le pigeon aux petits pois (The Pigeon with the Peas) by Pablo Picasso, La Pastorale by Henri Matisse, L'Olivier Près de l'Estaque (Olive Tree near Estaque) by Georges Braque,  (Woman with a Fan) by Amedeo Modigliani and Nature Morte aux Chandeliers (Still Life with Chandeliers) by Fernand Léger and were valued at €100 million ( $123 million USD). A window had been smashed and CCTV footage showed a masked man taking the paintings. Authorities believe the thief acted alone. The man carefully removed the paintings from their frames, which he left behind.

References and sources

 * References

 * Sources

 * Clement, Russell T. (1994). Georges Braque: A Bio-bibliography. Westport, Conn.:  Greenwood Press. ISBN 978-0-313-29235-4
 * Orozco, Miguel (2018) "The Complete Prints of Georges Braque. Catalogue raisonné". Academia.edu
 * Fry, Edward F. (1966). "Cubism 1907-1908: An Early Eyewitness Account". Art Bulletin 48: 71–73.
 * Mullins, Edwin (1968). The Art of Georges Braque. New York: Harry N. Abrams, Inc.
 * Solomon R. Guggenheim Museum
 * Picasso, P., Rubin, W. S., & Fluegel, J. (1980). Pablo Picasso, a retrospective. New York: Museum of Modern Art. ISBN 0-87070-528-8

title: Georges Braque


text:
Gilbert Cesbron

Gilbert Cesbron (13 January 1913, Paris – 12 August 1979, Paris) was a French novelist.

Biography
Gilbert Cesbron (13 January 1913, Paris – 12 August 1979, Paris) was a French novelist. Born in Paris, Cesbron attended what is now known as Lycée Condorcet. In 1944 he published his first novel, Les innocents de Paris ("The Innocent of Paris"), in Switzerland. He first achieved wide public acclaim with the publication of Notre prison est un royaume ("Our Prison is a Kingdom") in 1948 and Il est minuit, docteur Schweitzer ("It is midnight, Doctor Schweitzer") in 1950.

In his works Cesbron tended to illustrate and describe relevant social topics such as juvenile delinquency in Chiens perdus sans collier ("Lost Dogs Without Collars"), violence in Entre chiens et loups ("Between Dogs and Wolves"), euthanasia in Il est plus tard que tu ne penses ("It is Later than You Think") and working priests in Les Saints vont en enfer ("Saints in Hell").

In 1955, Cesbron's book Chiens perdus sans collier, the story of an orphan boy and a benevolent judge, was made into a movie starring Jean Gabin and Robert Dalban.

He died on 12 August 1979 at his home at 126 Boulevard Saint-Germain in the 6th arrondissement of Paris. He is buried in Bourré, Loir-et-Cher. His widow, Dominique, died in 2003.

Novels

 * Les Innocents de Paris, 1944.
 * On croit rêver (1945).
 * La Tradition Fontquernie (1947).
 * Notre prison est un royaume (1948).
 * La Souveraine (1949).
 * Bois mort où l'oiseau chante (1950).
 * Les saints vont en enfer (1952).
 * Chiens perdus sans collier (1954).
 * Vous verrez le ciel ouvert (1956).
 * Il est plus tard que tu ne penses (1958).
 * Avoir été (1960).
 * Entre chiens et loups (1962).
 * Une abeille contre la vitre (1964).
 * C’est Mozart qu’on assassine (1966).
 * Je suis mal dans ta peau (1969).
 * Voici le temps des imposteurs (1972).
 * Don Juan en automne (1975).
 * Mais moi je vous aimais (1977).
 * Compagnons de la nuit (1938, published in 1995).

Tales and short stories

 * D’Outremonde (23 tales), (1949).
 * Traduit du vent (1951).
 * Tout dort et je veille (1959).
 * La Ville couronnée d’épines (1964).
 * Des enfants aux cheveux gris (1968).
 * Un vivier sans eau (1979).
 * Leur pesant d’écume (1980) ;
 * Tant d’amour perdu (1981).

Essays

 * Chasseur maudit (1953).
 * Ce siècle appelle au secours (1955).
 * Libérez Barabbas (1957).
 * Une sentinelle attend l’aurore (1965).
 * Lettre ouverte à une jeune fille morte (1968).
 * Ce que je crois (1970).
 * Des leçons d’abîme (1971).
 * Mourir étonné (1976) ;
 * Huit paroles pour l’éternité (1978).
 * Passé un certain âge (1980).
 * La regarder en face (1982).

Plays

 * Il est minuit, docteur Schweitzer (1952)
 * Briser la statue (1952), raconte la vie de Sainte Thérèse de Lisieux.
 * L’Homme seul (1961).
 * Phèdre à Colombes (1961).
 * Dernier Acte (1961).
 * Mort le premier (1970).
 * Pauvre Philippe (1970)

Other

 * Torrent (poèmes) (1934).
 * Les Petits des Hommes (album de photos avec texte) (1954).
 * Il suffit d’aimer (récit de la vie de Sainte Bernadette Soubirous (1960).
 * Journal sans date (tome 1) (1963).
 *  Journal sans date, (tome 2). Tant qu’il fait jour (1967).
 *  Journal sans date, (tome 3). Un miroir en miettes (1973) ;
 * Merci l’oiseau ! (poèmes) (1976) ;
 * Ce qu’on appelle vivre (interviewed by the journalist Maurice Chavardès)(1977).
 * Bonheur de rien (1979).
 * Un désespoir allègre (1983).

Films

 * 1952 : Il est minuit, Docteur Schweitzer, director André Haguet, with Jean Debucourt, Pierre Fresnay, Jeanne Moreau, Jean Lanier.
 * 1955 : Chiens perdus sans collier, director Jean Delannoy, with Jean Gabin, Robert Dalban, Jean-Jacques Delbo.
 * 1960 : Il suffit d'aimer, director Robert Darène, script and dialogue Gilbert Cesbron, with Madeleine Sologne, music Maurice Thiriet.

Television

 * 1959 : Ruf ohne Echo, director Rainer Wolffhardt, with Horst Tappert, Hans Christian Blech.
 * 1962 : Il est minuit, Docteur Schweitzer, director Gilbert Pineau.
 * 1977 : C’est Mozart qu’on assassine, director Pierre Goutas, with Cyril Brisse, Henri Garcin, Catherine Rich, Louis Seigner.
 * 1979 : Avoir été, director Roland-Bernard.

title: Gilbert Cesbron