text:
Low-density parity-check code

In information theory, a low-density parity-check (LDPC) code is a linear error correcting code, a method of transmitting a message over a noisy transmission channel. An LDPC code is constructed using a sparse Tanner graph (subclass of the bipartite graph). LDPC codes are capacity-approaching codes, which means that practical constructions exist that allow the noise threshold to be set very close to the theoretical maximum (the Shannon limit) for a symmetric memoryless channel. The noise threshold defines an upper bound for the channel noise, up to which the probability of lost information can be made as small as desired. Using iterative belief propagation techniques, LDPC codes can be decoded in time linear in their block length.

LDPC codes are also known as Gallager codes, in honor of Robert G. Gallager, who developed the LDPC concept in his doctoral dissertation at the Massachusetts Institute of Technology in 1960. However, LDPC codes require computationally expensive iterative decoding, so they went unused for decades. In 1993 the newly invented turbo codes demonstrated that codes with iterative decoding could far outperform other codes used at that time, but turbo codes were patented and required a fee for use. This raised renewed interest in LDPC codes, which were shown to have similar performance, but were much older and patent-free. Now that the fundamental patent for turbo codes has expired (on August 29, 2013), LDPC codes are still used for their technical merits.

LDPC codes have been shown to have ideal combinatorial properties. In his dissertation, Gallager showed that LDPC codes achieve the Gilbert–Varshamov bound for linear codes over binary fields with high probability. In 2020 it was shown that Gallager's LDPC codes achieve list decoding capacity and also achieve the Gilbert–Varshamov bound for linear codes over general fields.

History
Impractical to implement when first developed by Gallager in 1963, LDPC codes were forgotten until his work was rediscovered in 1996. Turbo codes, another class of capacity-approaching codes discovered in 1993, became the coding scheme of choice in the late 1990s, used for applications such as the Deep Space Network and satellite communications. LDPC codes then received renewed interest as a patent-free alternative of similar performance. Since then, advances in low-density parity-check codes have seen them surpass turbo codes in terms of error floor and performance in the higher code rate range, leaving turbo codes better suited for the lower code rates only.

Applications
In 2003, an irregular repeat accumulate (IRA) style LDPC code beat six turbo codes to become the error-correcting code in the new DVB-S2 standard for digital television. The DVB-S2 selection committee made decoder complexity estimates for the turbo code proposals using a much less efficient serial decoder architecture rather than a parallel decoder architecture. This forced the turbo code proposals to use frame sizes on the order of one half the frame size of the LDPC proposals.

In 2008, LDPC beat convolutional turbo codes as the forward error correction (FEC) system for the ITU-T G.hn standard. G.hn chose LDPC codes over turbo codes because of their lower decoding complexity (especially when operating at data rates close to 1.0 Gbit/s) and because the proposed turbo codes exhibited a significant error floor at the desired range of operation.

LDPC codes are also used for 10GBASE-T Ethernet, which sends data at 10 gigabits per second over twisted-pair cables. As of 2009, LDPC codes are also part of the Wi-Fi 802.11 standard as an optional part of 802.11n and 802.11ac, in the High Throughput (HT) PHY specification. LDPC is a mandatory part of 802.11ax (Wi-Fi 6).

Some OFDM systems add an additional outer error correction that fixes the occasional errors (the "error floor") that get past the LDPC correction inner code even at low bit error rates.

For example: The Reed-Solomon code with LDPC Coded Modulation (RS-LCM) uses a Reed-Solomon outer code. The DVB-S2, the DVB-T2 and the DVB-C2 standards all use a BCH code outer code to mop up residual errors after LDPC decoding.

5G NR uses polar code for the control channels and LDPC for the data channels.

Although LDPC code has had its success in commercial hard disk drives, to fully exploit its error correction capability in SSDs demands unconventional fine-grained flash memory sensing, leading to an increased memory read latency. LDPC-in-SSD is an effective approach to deploy LDPC in SSD with a very small latency increase, which turns LDPC in SSD into a reality. Since then, LDPC has been widely adopted in commercial SSDs in both customer-grades and enterprise-grades by major storage venders. Many TLC (and later) SSDs are using LDPC codes. A fast hard-decode (binary erasure) is first attempted, which can fall back into the slower but more powerful soft decoding.

Operational use
LDPC codes functionally are defined by a sparse parity-check matrix. This sparse matrix is often randomly generated, subject to the sparsity constraints—LDPC code construction is discussed later. These codes were first designed by Robert Gallager in 1960.

Below is a graph fragment of an example LDPC code using Forney's factor graph notation. In this graph, n variable nodes in the top of the graph are connected to (n−k) constraint nodes in the bottom of the graph.

This is a popular way of graphically representing an (n, k) LDPC code. The bits of a valid message, when placed on the T's at the top of the graph, satisfy the graphical constraints. Specifically, all lines connecting to a variable node (box with an '=' sign) have the same value, and all values connecting to a factor node (box with a '+' sign) must sum, modulo two, to zero (in other words, they must sum to an even number; or there must be an even number of odd values).

Ignoring any lines going out of the picture, there are eight possible six-bit strings corresponding to valid codewords: (i.e., 000000, 011001, 110010, 101011, 111100, 100101, 001110, 010111). This LDPC code fragment represents a three-bit message encoded as six bits. Redundancy is used, here, to increase the chance of recovering from channel errors. This is a (6, 3) linear code, with n = 6 and k = 3.

Again ignoring lines going out of the picture, the parity-check matrix representing this graph fragment is

\mathbf{H} = \begin{pmatrix} 1 & 1 & 1 & 1 & 0 & 0 \\ 0 & 0 & 1 & 1 & 0 & 1 \\ 1 & 0 & 0 & 1 & 1 & 0 \\ \end{pmatrix}. $$

In this matrix, each row represents one of the three parity-check constraints, while each column represents one of the six bits in the received codeword.

In this example, the eight codewords can be obtained by putting the parity-check matrix H into this form $$\begin{bmatrix} -P^T | I_{n-k} \end{bmatrix}$$ through basic row operations in GF(2):
 * $$\mathbf{H}

= \begin{pmatrix} 1 & 1 & 1 & 1 & 0 & 0 \\ 0 & 0 & 1 & 1 & 0 & 1 \\ 1 & 0 & 0 & 1 & 1 & 0 \\ \end{pmatrix}_1 \sim \begin{pmatrix} 1 & 1 & 1 & 1 & 0 & 0 \\ 0 & 0 & 1 & 1 & 0 & 1 \\ 0 & 1 & 1 & 0 & 1 & 0 \\ \end{pmatrix}_2 \sim \begin{pmatrix} 1 & 1 & 1 & 1 & 0 & 0 \\ 0 & 1 & 1 & 0 & 1 & 0 \\ 0 & 0 & 1 & 1 & 0 & 1 \\ \end{pmatrix}_3 \sim \begin{pmatrix} 1 & 1 & 1 & 1 & 0 & 0 \\ 0 & 1 & 1 & 0 & 1 & 0 \\ 1 & 1 & 0 & 0 & 0 & 1 \\ \end{pmatrix}_4. $$

Step 1: H.

Step 2: Row 1 is added to row 3.

Step 3: Row 2 and 3 are swapped.

Step 4: Row 1 is added to row 3.

From this, the generator matrix G can be obtained as $$\begin{bmatrix} I_{k} | P \end{bmatrix}$$ (noting that in the special case of this being a binary code $$P = -P$$), or specifically:

 * $$\mathbf{G}

= \begin{pmatrix} 1 & 0 & 0 & 1 & 0 & 1 \\ 0 & 1 & 0 & 1 & 1 & 1 \\ 0 & 0 & 1 & 1 & 1 & 0 \\ \end{pmatrix}. $$

Finally, by multiplying all eight possible 3-bit strings by G, all eight valid codewords are obtained. For example, the codeword for the bit-string '101' is obtained by:

\begin{pmatrix} 1 & 0 & 1 \\ \end{pmatrix} \odot \begin{pmatrix} 1 & 0 & 0 & 1 & 0 & 1 \\ 0 & 1 & 0 & 1 & 1 & 1 \\ 0 & 0 & 1 & 1 & 1 & 0 \\ \end{pmatrix} = \begin{pmatrix} 1 & 0 & 1 & 0 & 1 & 1 \\ \end{pmatrix} $$,

where $$\odot$$ is symbol of mod 2 multiplication.

As a check, the row space of G is orthogonal to H such that $$ G \odot H^T = 0 $$

The bit-string '101' is found in as the first 3 bits of the codeword '101011'.

Example encoder

During the encoding of a frame, the input data bits (D) are repeated and distributed to a set of constituent encoders. The constituent encoders are typically accumulators and each accumulator is used to generate a parity symbol. A single copy of the original data (S0,K-1) is transmitted with the parity bits (P) to make up the code symbols. The S bits from each constituent encoder are discarded.

The parity bit may be used within another constituent code.

In an example using the DVB-S2 rate 2/3 code the encoded block size is 64800 symbols (N=64800) with 43200 data bits (K=43200) and 21600 parity bits (M=21600). Each constituent code (check node) encodes 16 data bits except for the first parity bit which encodes 8 data bits. The first 4680 data bits are repeated 13 times (used in 13 parity codes), while the remaining data bits are used in 3 parity codes (irregular LDPC code).

For comparison, classic turbo codes typically use two constituent codes configured in parallel, each of which encodes the entire input block (K) of data bits. These constituent encoders are recursive convolutional codes (RSC) of moderate depth (8 or 16 states) that are separated by a code interleaver which interleaves one copy of the frame.

The LDPC code, in contrast, uses many low depth constituent codes (accumulators) in parallel, each of which encode only a small portion of the input frame. The many constituent codes can be viewed as many low depth (2 state) "convolutional codes" that are connected via the repeat and distribute operations. The repeat and distribute operations perform the function of the interleaver in the turbo code.

The ability to more precisely manage the connections of the various constituent codes and the level of redundancy for each input bit give more flexibility in the design of LDPC codes, which can lead to better performance than turbo codes in some instances. Turbo codes still seem to perform better than LDPCs at low code rates, or at least the design of well performing low rate codes is easier for turbo codes.

As a practical matter, the hardware that forms the accumulators is reused during the encoding process. That is, once a first set of parity bits are generated and the parity bits stored, the same accumulator hardware is used to generate a next set of parity bits.

Decoding
As with other codes, the maximum likelihood decoding of an LDPC code on the binary symmetric channel is an NP-complete problem, shown by reduction from 3-dimensional matching. So assuming P != NP, which is widely believed, then performing optimal decoding for an arbitrary code of any useful size is not practical.

However, sub-optimal techniques based on iterative belief propagation decoding give excellent results and can be practically implemented. The sub-optimal decoding techniques view each parity check that makes up the LDPC as an independent single parity check (SPC) code. Each SPC code is decoded separately using soft-in-soft-out (SISO) techniques such as SOVA, BCJR, MAP, and other derivates thereof. The soft decision information from each SISO decoding is cross-checked and updated with other redundant SPC decodings of the same information bit. Each SPC code is then decoded again using the updated soft decision information. This process is iterated until a valid codeword is achieved or decoding is exhausted. This type of decoding is often referred to as sum-product decoding.

The decoding of the SPC codes is often referred to as the "check node" processing, and the cross-checking of the variables is often referred to as the "variable-node" processing.

In a practical LDPC decoder implementation, sets of SPC codes are decoded in parallel to increase throughput.

In contrast, belief propagation on the binary erasure channel is particularly simple where it consists of iterative constraint satisfaction.

For example, consider that the valid codeword, 101011, from the example above, is transmitted across a binary erasure channel and received with the first and fourth bit erased to yield ?01?11. Since the transmitted message must have satisfied the code constraints, the message can be represented by writing the received message on the top of the factor graph.

In this example, the first bit cannot yet be recovered, because all of the constraints connected to it have more than one unknown bit. In order to proceed with decoding the message, constraints connecting to only one of the erased bits must be identified. In this example, only the second constraint suffices. Examining the second constraint, the fourth bit must have been zero, since only a zero in that position would satisfy the constraint.

This procedure is then iterated. The new value for the fourth bit can now be used in conjunction with the first constraint to recover the first bit as seen below. This means that the first bit must be a one to satisfy the leftmost constraint.

Thus, the message can be decoded iteratively. For other channel models, the messages passed between the variable nodes and check nodes are real numbers, which express probabilities and likelihoods of belief.

This result can be validated by multiplying the corrected codeword r by the parity-check matrix H:

 * $$\mathbf{z} = \mathbf{H \odot r}

= \begin{pmatrix} 1 & 1 & 1 & 1 & 0 & 0 \\ 0 & 0 & 1 & 1 & 0 & 1 \\ 1 & 0 & 0 & 1 & 1 & 0 \\ \end{pmatrix} \odot \begin{pmatrix} 1 \\ 0 \\ 1 \\ 0 \\ 1 \\ 1 \\ \end{pmatrix}

= \begin{pmatrix} 0 \\ 0 \\ 0 \\ \end{pmatrix}. $$

Because the outcome z (the syndrome) of this operation is the three × one zero vector, the resulting codeword r is successfully validated.

After the decoding is completed, the original message bits '101' can be extracted by looking at the first 3 bits of the codeword.

While illustrative, this erasure example does not show the use of soft-decision decoding or soft-decision message passing, which is used in virtually all commercial LDPC decoders.

Updating node information
In recent years, there has also been a great deal of work spent studying the effects of alternative schedules for variable-node and constraint-node update. The original technique that was used for decoding LDPC codes was known as flooding. This type of update required that, before updating a variable node, all constraint nodes needed to be updated and vice versa. In later work by Vila Casado et al., alternative update techniques were studied, in which variable nodes are updated with the newest available check-node information.

The intuition behind these algorithms is that variable nodes whose values vary the most are the ones that need to be updated first. Highly reliable nodes, whose log-likelihood ratio (LLR) magnitude is large and does not change significantly from one update to the next, do not require updates with the same frequency as other nodes, whose sign and magnitude fluctuate more widely. These scheduling algorithms show greater speed of convergence and lower error floors than those that use flooding. These lower error floors are achieved by the ability of the Informed Dynamic Scheduling (IDS) algorithm to overcome trapping sets of near codewords.

When nonflooding scheduling algorithms are used, an alternative definition of iteration is used. For an (n, k) LDPC code of rate k/n, a full iteration occurs when n variable and n − k constraint nodes have been updated, no matter the order in which they were updated.

Code construction
For large block sizes, LDPC codes are commonly constructed by first studying the behaviour of decoders. As the block size tends to infinity, LDPC decoders can be shown to have a noise threshold below which decoding is reliably achieved, and above which decoding is not achieved, colloquially referred to as the cliff effect. This threshold can be optimised by finding the best proportion of arcs from check nodes and arcs from variable nodes. An approximate graphical approach to visualising this threshold is an EXIT chart.

The construction of a specific LDPC code after this optimization falls into two main types of techniques:

 * Pseudorandom approaches
 * Combinatorial approaches

Construction by a pseudo-random approach builds on theoretical results that, for large block size, a random construction gives good decoding performance. In general, pseudorandom codes have complex encoders, but pseudorandom codes with the best decoders can have simple encoders. Various constraints are often applied to help ensure that the desired properties expected at the theoretical limit of infinite block size occur at a finite block size.

Combinatorial approaches can be used to optimize the properties of small block-size LDPC codes or to create codes with simple encoders.

Some LDPC codes are based on Reed–Solomon codes, such as the RS-LDPC code used in the 10 Gigabit Ethernet standard. Compared to randomly generated LDPC codes, structured LDPC codes—such as the LDPC code used in the DVB-S2 standard—can have simpler and therefore lower-cost hardware—in particular, codes constructed such that the H matrix is a circulant matrix.

Yet another way of constructing LDPC codes is to use finite geometries. This method was proposed by Y. Kou et al. in 2001.

Compared to turbo codes
LDPC codes can be compared with other powerful coding schemes, e.g. turbo codes. In one hand, BER performance of turbo codes is influenced by low codes limitations. LDPC codes have no limitations of minimum distance, that indirectly means that LDPC codes may be more efficient on relatively large code rates (e.g. 3/4, 5/6, 7/8) than turbo codes. However, LDPC codes are not the complete replacement: turbo codes are the best solution at the lower code rates (e.g. 1/6, 1/3, 1/2).

People

 * Richard Hamming
 * Claude Shannon
 * David J. C. MacKay
 * Irving S. Reed
 * Michael Luby

Theory

 * Graph theory
 * Hamming code
 * Sparse graph code
 * Expander code

Applications

 * G.hn/G.9960 (ITU-T Standard for networking over power lines, phone lines and coaxial cable)
 * 802.3an or 10GBASE-T (10 gigabit/s Ethernet over twisted pair)
 * CMMB (China Multimedia Mobile Broadcasting)
 * DVB-S2 / DVB-T2 / DVB-C2 (digital video broadcasting, 2nd generation)
 * DMB-T/H (digital video broadcasting)
 * WiMAX (IEEE 802.16e standard for microwave communications)
 * IEEE 802.11n-2009 (Wi-Fi standard)
 * DOCSIS 3.1
 * ATSC 3.0 (Next generation North America digital terrestrial broadcasting)
 * 3GPP (5G-NR data channel)

Other capacity-approaching codes

 * Fountain codes
 * LT codes
 * Online codes
 * Raptor codes
 * Repeat-accumulate codes (a class of simple turbo codes)
 * Serial concatenated convolutional codes
 * Tornado codes (LDPC codes designed for erasure decoding)
 * Turbo codes

Capacity-achieving codes
So far there is only one capacity achieving code by design and proof.
 * Polar codes

title: Low-density parity-check code


text:
1919 Quebec general election

The 1919 Quebec general election was held on June 23, 1919, to elect members of the 15th Legislative Assembly of Quebec, Canada. The incumbent Quebec Liberal Party, led by Lomer Gouin, was re-elected, defeating the Quebec Conservative Party, led by Arthur Sauvé.

Gouin, who had held office since 1905, resigned precisely one year after the election to make way for his successor Louis-Alexandre Taschereau. Gouin himself had originally come to power in much the same way, after his predecessor Simon-Napoléon Parent resigned soon after winning his final election.

Results
!rowspan="2" colspan="2"|Party !rowspan="2"|Party leader !rowspan="2"|Candidates !colspan="3"|Seats !colspan="4"|Popular Vote !1916 !Elected !± !# !± !% !± (pp)

 * Lomer Gouin
 * 79
 * 75
 * 74
 * 1
 * 67,292
 * 58,974
 * 51.91
 * 8.66

 * Arthur Sauvé
 * 20
 * 6
 * 5
 * 1
 * 21,990
 * 73,147
 * 16.96
 * 18.13
 * style="background-color:#EEBBBB;" |
 * style="text-align:left;" | Parti ouvrier
 * 7
 * 2
 * 2
 * 12,506
 * 10,674
 * 9.65
 * 8.77
 * 10,674
 * 9.65
 * 8.77

 * 22
 * 21,902
 * 14,695
 * 16.88
 * 13.42
 * style="background-color:lightcoral;" |
 * style="text-align:left;" |Liberal-Democrat
 * 5
 * 4,399
 * New
 * 3.38
 * New
 * 5
 * 4,399
 * New
 * 3.38
 * New
 * 4,399
 * New
 * 3.38
 * New

! colspan="3" style="text-align:left;" | Total ! " colspan="3"| 81 ! " colspan="2"| 129,636 ! " colspan="2"| 100%
 * 1
 * 1,457
 * New
 * 1.12
 * New
 * 1,457
 * New
 * 1.12
 * New
 * 134
 * colspan="7" style="text-align:left;" | Rejected ballots
 * 1,448
 * 1,319
 * colspan="2"|
 * colspan="7" style="text-align:left;" | Voter turnout
 * 131,184
 * 80,035
 * 55.11
 * 7.44
 * colspan="7" style="text-align:left;" | Registered electors (contested ridings only)
 * 238,052
 * 99,644
 * colspan="2"|
 * colspan="5" style="text-align:left;" | Candidates returned by acclamation
 * 45
 * 19
 * colspan="4"|
 * }
 * 45
 * 19
 * colspan="4"|
 * }

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

title: 1919 Quebec general election


text:
Video game genre

A video game genre is an informal classification of a video game based on how it is played rather than visual or narrative elements. This is independent of setting, unlike works of fiction that are expressed through other media, such as films or books. For example, a shooter game is still a shooter game, regardless of where or when it takes place. A specific game's genre is open to subjective interpretation. An individual game may belong to several genres at once.

History
Early attempts at categorizing video games were primarily for organizing catalogs and books. A 1981 catalog for the Atari VCS uses 8 headings: Skill Gallery, Space Station, Classics Corner, Adventure Territory, Race Track, Sports Arena, Combat Zone, and Learning Center. ("Classics", in this case, refers to chess and checkers.) In Tom Hirschfeld's 1981 book How to Master the Video Games, he divides the games into broad categories in the table of contents: Space Invaders-type, Asteroids-type, maze, reflex, and miscellaneous. The first two of these correspond to the still-used genres of fixed shooter and multidirectional shooter.

Within the personal computer space, two publications established a small number of categories based on the best-selling software in the early 1980s: Softalk, which ran its Top Thirty list from 1980 to 1984 with the genres of strategy, adventure, fantasy and arcade; and Computer Gaming World, which collected user-submitted rankings. Computer Gaming World initially used three categories in 1981—arcade, wargame, and adventure—but by 1989 had expanded its genre list to strategy, simulation, adventure, role-playing adventure, wargame, and action/arcade. Comparisons between computer and console games showed that players on computers tended to prefer more strategic games rather than action.

Chris Crawford attempted to classify video games in his 1984 book The Art of Computer Game Design. Crawford focused on the player's experience and activities required for gameplay. He wrote, "the state of computer game design is changing quickly. We would therefore expect the taxonomy presented [in this book] to become obsolete or inadequate in a short time."

Nintendo, in bringing its Famicom system into the North American market as the Nintendo Entertainment System in 1985, looked to avoid the issues with loss of publishing control that had led to the 1983 video game crash and to prevent unauthorized games from being released for the system. To solve this, Nintendo required approval of all games for the NES. To support this, Nintendo classified games into eight major series: Adventure, Action, Sports, Light-Gun, Programmable, Arcade, Robot, and Educational. The series description appeared on early "black box" covers and subsequently in the NES Player's Guide. By the time of the Game Boy and Super Nintendo Entertainment System, Nintendo had retired the Arcade, Light-Gun, Robot, Programmable, and Educational series, but added RPG & Simulation and Puzzle.

Consoles manufacturers that followed the NES followed similar behavior in requiring licenses to develop games for their systems. To assure they would get these licenses, console developers tended to stay with gameplay of previously published games for that console, thus causing groups of games within the same genre to grow. Subsequently, retailers displayed games grouped by genres, and market research firms found that players had preferences for certain types over others, based on region, and developers could plan out future strategies through this.

With the industry expanding in the 1990s and budgets for video games began growing, large publishers like Electronic Arts began to form to handle the marketing and publication of games, both for consoles and personal computers. Targeting high-value, low-risk video game genres were key for some publishers, and small and independent developers were typically forced to compete by abandoning more experimental gameplay and settling into the same genres used by larger publishers.

As hardware capabilities have increased, new genres have become possible, with examples being increased memory, the move from 2D to 3D, new peripherals, online functionalities, and location-based mechanics. Experimental gameplay from indie game development drew more attention in the late 2000s and 2010s aided by independent digital distribution, as large publishers focused on triple-A titles were extremely risk-averse. Through indie games, a revival of experimental gameplay had emerged, and several new genres have emerged since then.

Definition

Due to "direct and active participation" of the player, video game genres differ from literary and film genres. Though one could state that Space Invaders is a science fiction video game, author Mark J.P. Wolf wrote that such a classification "ignores the fundamental differences and similarities which are to be found in the player's experience of the game". In contrast to the visual aesthetics of games, which can vary greatly, it is argued that it is interactivity characteristics that are common to all games.

Like film genres, the names of video game genres have come about generally as a common understanding between the audience and the producers. Descriptive names of genres take into account the goals of the game, the protagonist and even the perspective offered to the player. For example, a first-person shooter is a game that is played from a first-person perspective and involves the practice of shooting. Whereas "shooter game" is a genre name, "first-person shooter" and "third-person shooter" are common subgenres of the shooter genre. Other examples of such prefixes are real-time, turn based, top-down and side-scrolling.

Genre names may evolve over time. The platform game genre started as "climbing games", based on Steve Bloom's 1982 book Video Invaders, as they were inspired by games like Donkey Kong with ladders and jumping. The same term was used by the US and UK press in 1983, including magazines Electronic Games and TV Gamer. First-person shooters were originally known as "Doom clones" in the years following 1993's Doom, while the term "first-person shooters" became more common by around 2000.

New genres emerge continuously throughout the history of video games, often due to the cross-pollination of ideas borrowed from different games into new ones. For example, the seminal text-based adventure game Colossal Cave Adventure directly inspired the Atari VCS game Adventure, but incorporating joystick control as in an action game rather than typed commands. Adventure served as the prototype of the action-adventure game genre that would be popularized by The Legend of Zelda.

The target audience, underlying theme or purpose of a game are sometimes used as a genre identifier, such as with "Christian game" and "serious game" respectively. However, because these terms do not indicate anything about the gameplay of a video game, these are not considered genres.

Classifications
Video game genres vary in specificity, with popular video game reviews using genre names varying from "action" to "baseball". In this practice, basic themes and more fundamental characteristics are used alongside each other.

A game may combine aspects of multiple genres in such a way that it becomes hard to classify under existing genres. For example, because Grand Theft Auto III combined shooting, driving and roleplaying in an unusual way, it was hard to classify using existing terms. The term Grand Theft Auto clone has been used to describe games mechanically similar to Grand Theft Auto III. Similarly, the term roguelike has been developed for games that share similarities with Rogue.

Elements of the role-playing genre, which focuses on storytelling and character growth, have been implemented in many different genres of video games. This is because the addition of a story and character enhancement to an action, strategy or puzzle video game does not take away from its core gameplay, but adds an incentive other than survival to the experience.

In addition to gameplay elements, some games may be categorized by other schemes; such are typically not used as genres:
 * By platform: generally to the nature of the computer hardware that the game is played on and not the specific branding. This would include game genres like mobile games for smartphone, tablet computers, or other similar portable devices; and browser games that can be played in a web browser. Identification of the type of hardware a game is played on implied certain limits to the type of gameplay that is available; a mobile game will typically lack as much action compared to a game playable on a home console or computer due to limitations on player input.
 * By mode: referring to whether a game is single player, multiplayer, or variations on that, including massively multiplayer online (MMO) games, cooperative games, player versus environment (PvE) or player versus player (PvP) games, and so forth.
 * By narrative: Classifying video games by their narrative style, such as science fiction or fantasy, is typically not used within the field, with the key exception of horror games, which broadly cover any game dealing with elements of horror fiction.

Popularity
According to some analysts, the percentage of each broad genre in the best-selling physical games worldwide is broken down as follows.

In the last decade, puzzle games have declined when measured by sales, however, on mobile, where the majority of games are free-to-play, this genre remains the most popular worldwide.

title: Video game genre


text:
1916 Quebec general election

The 1916 Quebec general election was held on May 22, 1916, to elect members of the 14th Legislative Assembly of the Province of Quebec, Canada. The incumbent Quebec Liberal Party, led by Lomer Gouin, was re-elected, defeating the Quebec Conservative Party, led by Philémon Cousineau.

title: 1916 Quebec general election


text:
1912 Quebec general election

The 1912 Quebec general election was held on May 15, 1912, to elect members of the 13th Legislative Assembly of the Province of Quebec, Canada. The incumbent Quebec Liberal Party, led by Lomer Gouin, was re-elected, defeating the Quebec Conservative Party, led by Joseph-Mathias Tellier.

Redistribution of ridings
An Act passed prior to the election increased the number of MLAs from 74 to 81 through the following changes:

title: 1912 Quebec general election


text:
1908 Quebec general election

The 1908 Quebec general election was held on June 8, 1908, to elect members of the 12th Legislative Assembly of the Province of Quebec, Canada. The incumbent Quebec Liberal Party, led by Lomer Gouin, was re-elected, defeating the Quebec Conservative Party, led by Pierre-Évariste Leblanc.

title: 1908 Quebec general election


text:
Chesterfield, New Jersey

Chesterfield, originally known as Recklesstown, is an unincorporated community located around the intersection of County Route 528 (Bordentown-Chesterfield Road, Chesterfield-Arneytown Road) and County Route 677 (Chesterfield-Georgetown Road) in Chesterfield Township of Burlington County, New Jersey.

History
In the 1830s, the village had a store, hotel, church, and post office. The village was originally named after Joseph Reckless, who had bought a mill here in 1712. His grandsons, Anthony and Robert, served in the American Revolutionary War. The name of the community was changed to Chesterfield in 1888 by congressman Anthony Bullock. The oldest part of the Recklesstown Tavern, now the Chesterfield Inn, was built c. 1710. The tavern was expanded in 1774.

Historic district
The Recklesstown Historic District is a 200 acre historic district encompassing the village. It was added to the National Register of Historic Places on August 19, 1975, for its significance in agriculture, religion, and transportation. The district includes 49 contributing buildings. The Kessler House is a two and one-half story brick building built c. 1849. The Chesterfield Baptist Church was built in 1848 and features Greek Doric columns. Across the street is the Clayton House, once the church rectory, now a florist.

Notable people

 * Charles Newbold (1764–1835), blacksmith, invented the first one piece cast iron plow, patented in 1797

title: Chesterfield, New Jersey


text:
User:Love over Money

This campaign will continue until the themes are appreciated in every major media market in the nations that use this web site.

title: User:Love over Money


text:
1904 Quebec general election

The 1904 Quebec general election was held on November 25, 1904, to elect members of the Legislative Assembly of the Province of Quebec, Canada. The incumbent Quebec Liberal Party, led by Simon-Napoléon Parent, was re-elected, defeating the Quebec Conservative Party, led by Edmund James Flynn.

It was Parent's final election. Due to internal dissension within his party, he resigned in 1905, and was succeeded as Liberal leader and premier by Lomer Gouin.

title: 1904 Quebec general election


text:
Monochromator

A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input. The name is from the Greek roots mono-, "single", and chroma, "colour", and the Latin suffix -ator, denoting an agent.

Uses
A device that can produce monochromatic light has many uses in science and in optics because many optical characteristics of a material are dependent on wavelength. Although there are a number of useful ways to select a narrow band of wavelengths (which, in the visible range, is perceived as a pure color), there are not as many other ways to easily select any wavelength band from a wide range. See below for a discussion of some of the uses of monochromators.

In hard X-ray and neutron optics, crystal monochromators are used to define wave conditions on the instruments.

Techniques
A monochromator can use either the phenomenon of optical dispersion in a prism, or that of diffraction using a diffraction grating, to spatially separate the colors of light. It usually has a mechanism for directing the selected color to an exit slit. Usually the grating or the prism is used in a reflective mode. A reflective prism is made by making a right triangle prism (typically, half of an equilateral prism) with one side mirrored. The light enters through the hypotenuse face and is reflected back through it, being refracted twice at the same surface. The total refraction, and the total dispersion, is the same as would occur if an equilateral prism were used in transmission mode.

Collimation
The dispersion or diffraction is only controllable if the light is collimated, that is if all the rays of light are parallel, or practically so. A source, like the sun, which is very far away, provides collimated light. Newton used sunlight in his famous experiments. In a practical monochromator, however, the light source is close by, and an optical system in the monochromator converts the diverging light of the source to collimated light. Although some monochromator designs do use focusing gratings that do not need separate collimators, most use collimating mirrors. Reflective optics are preferred because they do not introduce dispersive effects of their own.

Geometrical design of a prism or grating monochromator
There are grating/prism configurations that offer different tradeoffs between simplicity and spectral accuracy.
 * Czerny–Turner (discussed below)
 * Paschen-Runge
 * Eagle
 * Wadsworth
 * Ebert-Fasti
 * Littrow
 * Pfund

In the common Czerny–Turner design, the broad-band illumination source (A) is aimed at an entrance slit (B). The amount of light energy available for use depends on the intensity of the source in the space defined by the slit (width × height) and the acceptance angle of the optical system. The slit is placed at the effective focus of a curved mirror (the collimator, C) so that the light from the slit reflected from the mirror is collimated (focused at infinity). The collimated light is diffracted from the grating (D) and then is collected by another mirror (E), which refocuses the light, now dispersed, on the exit slit (F). In a prism monochromator, a reflective Littrow prism takes the place of the diffraction grating, in which case the light is refracted by the prism.

At the exit slit, the colors of the light are spread out (in the visible this shows the colors of the rainbow). Because each color arrives at a separate point in the exit-slit plane, there are a series of images of the entrance slit focused on the plane. Because the entrance slit is finite in width, parts of nearby images overlap. The light leaving the exit slit (F) contains the entire image of the entrance slit of the selected color plus parts of the entrance slit images of nearby colors. A rotation of the dispersing element causes the band of colors to move relative to the exit slit, so that the desired entrance slit image is centered on the exit slit. The range of colors leaving the exit slit is a function of the width of the slits. The entrance and exit slit widths are adjusted together.

Stray light
The ideal transfer function of such a monochromator is a triangular shape. The peak of the triangle is at the nominal wavelength selected. The intensity of the nearby colors then decreases linearly on either side of this peak until some cutoff value is reached, where the intensity stops decreasing. This is called the stray light level. The cutoff level is typically about one thousandth of the peak value, or 0.1%.

Spectral bandwidth
Spectral bandwidth is defined as the width of the triangle at the points where the light has reached half the maximum value (full width at half maximum, abbreviated as FWHM). A typical spectral bandwidth might be one nanometer; however, different values can be chosen to meet the need of analysis. A narrower bandwidth does improve the resolution, but it also decreases the signal-to-noise ratio.

Dispersion
The dispersion of a monochromator is characterized as the width of the band of colors per unit of slit width, 1 nm of spectrum per mm of slit width for instance. This factor is constant for a grating, but varies with wavelength for a prism. If a scanning prism monochromator is used in a constant bandwidth mode, the slit width must change as the wavelength changes. Dispersion depends on the focal length, the grating order and grating resolving power.

Wavelength range
A monochromator's adjustment range might cover the visible spectrum and some part of both or either of the nearby ultraviolet (UV) and infrared (IR) spectra, although monochromators are built for a great variety of optical ranges, and to a great many designs.

Double monochromators
It is common for two monochromators to be connected in series, with their mechanical systems operating in tandem so that they both select the same color. This arrangement is not intended to improve the narrowness of the spectrum, but rather to lower the cutoff level. A double monochromator may have a cutoff about one millionth of the peak value, the product of the two cutoffs of the individual sections. The intensity of the light of other colors in the exit beam is referred to as the stray light level and is the most critical specification of a monochromator for many uses. Achieving low stray light is a large part of the art of making a practical monochromator.

Diffraction gratings and blazed gratings
Grating monochromators disperse ultraviolet, visible, and infrared radiation typically using replica gratings, which are manufactured from a master grating. A master grating consists of a hard, optically flat, surface that has a large number of parallel and closely spaced grooves. The construction of a master grating is a long, expensive process because the grooves must be of identical size, exactly parallel, and equally spaced over the length of the grating (3–10 cm). A grating for the ultraviolet and visible region typically has 300–2000 grooves/mm, however 1200–1400 grooves/mm is most common. For the infrared region, gratings usually have 10–200 grooves/mm. When a diffraction grating is used, care must be taken in the design of broadband monochromators because the diffraction pattern has overlapping orders. Sometimes broadband preselector filters are inserted in the optical path to limit the width of the diffraction orders so they do not overlap. Sometimes this is done by using a prism as one of the monochromators of a dual monochromator design.

The original high-resolution diffraction gratings were ruled. The construction of high-quality ruling engines was a large undertaking (as well as exceedingly difficult, in past decades), and good gratings were very expensive. The slope of the triangular groove in a ruled grating is typically adjusted to enhance the brightness of a particular diffraction order. This is called blazing a grating. Ruled gratings have imperfections that produce faint "ghost" diffraction orders that may raise the stray light level of a monochromator. A later photolithographic technique allows gratings to be created from a holographic interference pattern. Holographic gratings have sinusoidal grooves and so are not as bright, but have lower scattered light levels than blazed gratings. Almost all the gratings actually used in monochromators are carefully made replicas of ruled or holographic master gratings.

Prisms
Prisms have higher dispersion in the UV region. Prism monochromators are favored in some instruments that are principally designed to work in the far UV region. Most monochromators use gratings, however. Some monochromators have several gratings that can be selected for use in different spectral regions. A double monochromator made by placing a prism and a grating monochromator in series typically does not need additional bandpass filters to isolate a single grating order.

Focal length
The narrowness of the band of colors that a monochromator can generate is related to the focal length of the monochromator collimators. Using a longer focal length optical system also unfortunately decreases the amount of light that can be accepted from the source. Very high resolution monochromators might have a focal length of 2 meters. Building such monochromators requires exceptional attention to mechanical and thermal stability. For many applications a monochromator of about 0.4 meters' focal length is considered to have excellent resolution. Many monochromators have a focal length less than 0.1 meters.

Slit height
The most common optical system uses spherical collimators and thus contains optical aberrations that curve the field where the slit images come to focus, so that slits are sometimes curved instead of simply straight, to approximate the curvature of the image. This allows taller slits to be used, gathering more light, while still achieving high spectral resolution. Some designs take another approach and use toroidal collimating mirrors to correct the curvature instead, allowing higher straight slits without sacrificing resolution.

Wavelength vs. energy
Monochromators are often calibrated in units of wavelength. Uniform rotation of a grating produces a sinusoidal change in wavelength, which is approximately linear for small grating angles, so such an instrument is easy to build. Many of the underlying physical phenomena being studied are linear in energy though, and since wavelength and photon energy have a reciprocal relationship, spectral patterns that are simple and predictable when plotted as a function of energy are distorted when plotted as a function of wavelength. Some monochromators are calibrated in units of reciprocal centimeters or some other energy units, but the scale may not be linear.

Dynamic range
A spectrophotometer built with a high quality double monochromator can produce light of sufficient purity and intensity that the instrument can measure a narrow band of optical attenuation of about one million fold (6 AU, Absorbance Units).

Applications
Monochromators are used in many optical measuring instruments and in other applications where tunable monochromatic light is wanted. Sometimes the monochromatic light is directed at a sample and the reflected or transmitted light is measured. Sometimes white light is directed at a sample and the monochromator is used to analyze the reflected or transmitted light. Two monochromators are used in many fluorometers; one monochromator is used to select the excitation wavelength and a second monochromator is used to analyze the emitted light.

An automatic scanning spectrometer includes a mechanism to change the wavelength selected by the monochromator and to record the resulting changes in the measured quantity as a function of the wavelength.

If an imaging device replaces the exit slit, the result is the basic configuration of a spectrograph. This configuration allows the simultaneous analysis of the intensities of a wide band of colors. Photographic film or an array of photodetectors can be used, for instance to collect the light. Such an instrument can record a spectral function without mechanical scanning, although there may be tradeoffs in terms of resolution or sensitivity for instance.

An absorption spectrophotometer measures the absorption of light by a sample as a function of wavelength. Sometimes the result is expressed as percent transmission and sometimes it is expressed as the inverse logarithm of the transmission. The Beer–Lambert law relates the absorption of light to the concentration of the light-absorbing material, the optical path length, and an intrinsic property of the material called molar absorptivity. According to this relation the decrease in intensity is exponential in concentration and path length. The decrease is linear in these quantities when the inverse logarithm of transmission is used. The old nomenclature for this value was optical density (OD), current nomenclature is absorbance units (AU). One AU is a tenfold reduction in light intensity. Six AU is a millionfold reduction.

Absorption spectrophotometers often contain a monochromator to supply light to the sample. Some absorption spectrophotometers have automatic spectral analysis capabilities.

Absorption spectrophotometers have many everyday uses in chemistry, biochemistry, and biology. For example, they are used to measure the concentration or change in concentration of many substances that absorb light. Critical characteristics of many biological materials, many enzymes for instance, are measured by starting a chemical reaction that produces a color change that depends on the presence or activity of the material being studied. Optical thermometers have been created by calibrating the change in absorbance of a material against temperature. There are many other examples.

Spectrophotometers are used to measure the specular reflectance of mirrors and the diffuse reflectance of colored objects. They are used to characterize the performance of sunglasses, laser protective glasses, and other optical filters. There are many other examples.

In the UV, visible and near IR, absorbance and reflectance spectrophotometers usually illuminate the sample with monochromatic light. In the corresponding IR instruments, the monochromator is usually used to analyze the light coming from the sample.

Monochromators are also used in optical instruments that measure other phenomena besides simple absorption or reflection, wherever the color of the light is a significant variable. Circular dichroism spectrometers contain a monochromator, for example.

Lasers produce light which is much more monochromatic than the optical monochromators discussed here, but only some lasers are easily tunable, and these lasers are not as simple to use.

Monochromatic light allows for the measurement of the quantum efficiency (QE) of an imaging device (e.g. CCD or CMOS imager). Light from the exit slit is passed either through diffusers or an integrating sphere on to the imaging device while a calibrated detector simultaneously measures the light. Coordination of the imager, calibrated detector, and monochromator allows one to calculate the carriers (electrons or holes) generated for a photon of a given wavelength, QE.

title: Monochromator


text:
User talk:Moningka

Hi Wiki, this is a test to get a feeling how the editing looks. I'm from Indonesia, and just find this is amazing pages for global community to collaborate and grow.

title: User talk:Moningka


text:
Tef

Tef or TEF may refer to:

 * Eragrostis tef, a cereal from Ethiopia
 * Teaching Excellence Framework, a UK government assessment of the quality of undergraduate teaching in universities
 * Telefónica (stock symbol )
 * Tennessee Ernie Ford (1919–1991), American singer
 * Test d'évaluation du français, a test of fluency in French
 * The Elias Fund, a nonprofit organization empowering development in Zimbabwean youth
 * The Endless Forest, an online game
 * Thermic effect of food, an increment of energy expenditure
 * TEF (gene), Thyrotrophic embryonic factor, a human gene
 * Total enclosure fetishism, a form of sexual fetishism
 * Toxic equivalency factor for dioxins and dioxin-like compounds
 * Tracheoesophageal fistula, a medical condition
 * Transeuropa Ferries, a defunct ferry operator
 * Textual Editing Framework, a textual modeling tool for the Eclipse Modeling Framework software engineering facility
 * Telfer Airport, IATA airport code "TEF"

title: Tef


text:
Adriana La Cerva

Adriana La Cerva is a fictional character on the HBO TV series The Sopranos, portrayed by Drea de Matteo. She is the long-time girlfriend and, later, fiancée of Tony Soprano's protégé, Christopher Moltisanti. For her performance, de Matteo won the 2004 Emmy Award for Outstanding Supporting Actress in a Drama Series.

Character history
Adriana is the niece of Jackie and Richie Aprile. She is not repulsed by the Mafia lifestyle and starts out as a hostess at Artie Bucco's restaurant, Vesuvio. Adriana is initially portrayed as shallow and materialistic, interested in the things that her boyfriend Christopher's money could buy: expensive cars, shoes, jewelry, drugs, and designer clothing. Despite the couple growing closer, she becomes a frequent victim of domestic violence at the hands of Christopher.

After he and Adriana fight, she moves in with her mother, but Chris gets her back by proposing to her, against her mother's advice. Despite this, the two do not get married. She reveals to Chris that she is potentially infertile, which leads to another bout of domestic violence. Despite the violence, she always seems to have Christopher's best interests (as well as her own) in mind.

Adriana is portrayed as ambitious and wanting to have a business of her own. In Season 3, Christopher acquires The Lollipop Lounge in Long Branch, New Jersey, from a gambling debtor, and turns it over to Adriana to manage as she pleases. Adriana renames the bar "Crazy Horse" and makes it successful as a venue for local alternative rock bands and as a bar for college students from nearby Monmouth University and elsewhere. Benny Fazio is beaten in the nightclub's parking lot by Phil Leotardo. In season 4, Adriana reveals that she is possibly infertile due to complications from a previous abortion. In season 5, Adriana is diagnosed with ulcerative colitis.

The mole
By the end of season 3, The Federal Bureau of Investigation (FBI) targets Adriana as a potential witness in the family's organization. Upon the death of Sal "Big Pussy" Bonpensiero, the FBI looks to Adriana as a close relation to Christopher, a rising star in the crime family, and sends Special Agent Deborah Ciccerone to befriend her in "Army of One". Ciccerone, who goes by "Danielle Ciccolella", succeeds at befriending Adriana, but the FBI have to abandon the mission earlier than planned when Christopher makes a pass at Ciccerone, upsetting Adriana.

In "No Show", the FBI brings Adriana in and threatens her with long imprisonment for drug possession, or perhaps punishment by Tony Soprano, if she does not co-operate. Adriana vomits all over herself, the table, and the agents.

Out of loyalty to Christopher, Adriana avoids giving up any serious information on the family and does her best to avoid the Soprano family house in order to have nothing to give back to the FBI. In "Long Term Parking", her deception catches up with her after the FBI learns of her involvement in covering up a murder at her club. The FBI threatens to press charges of being an accessory to murder against her unless she offers full cooperation. Adriana refuses to wear a wire, instead asking the FBI for a chance to bring Christopher in with her and cooperate together.

She reveals the truth to Christopher, hoping they can go into the Witness Protection Program together and start new lives. An enraged Christopher beats and almost strangles her, before breaking down crying. His loyalty to his crime family turns out to be greater than his love for Adriana, and he reveals her status as an informant to Tony. Tony telephones Adriana, falsely informing her that Christopher attempted suicide at a diner in Ramapo Mountain State Forest before being found by the New Jersey State Police and has been hospitalized, and that Silvio Dante will drive her to the hospital.

En route on Interstate 287, Silvio stops the car in the middle of the woods. Realizing what is about to happen, a terrified Adriana tries to flee, crawling away from the car on all fours off screen where Silvio shoots her dead. Christopher is later seen putting some of her clothes in a red suitcase and dumping them. He then leaves her light blue Ford Thunderbird in the long-term parking lot at Newark Liberty International Airport.

Post-mortem
In the season 6 episode "The Ride", Carmela Soprano runs in to Adriana's mother, Liz La Cerva, who tells Carmela that she believes Christopher killed Adriana and that the FBI questioned her about Adriana's disappearance. When Carmela tells Tony about their conversation, he dismisses her fears, explaining that if Christopher had killed Adriana then her body would have been found by now. In addition, he points out to Carmela that if the FBI really suspected Christopher, then they would have arrested him.

While in Paris, Carmela dreams of seeing Adriana in a park, but a policeman tells her Adriana is dead. Carmela is intent on finding her, especially after Liz La Cerva tries to kill herself. However, Tony and Silvio pull some strings and Carmela is able to continue construction on her spec house, and the distraction keeps her from investigating the matter further.

title: Adriana La Cerva


text:
1900 Quebec general election

The 1900 Quebec general election was held on December 7, 1900, to elect members of the Legislative Assembly of the Province of Quebec, Canada. The incumbent Quebec Liberal Party, led by Simon-Napoléon Parent, was re-elected, defeating the Quebec Conservative Party, led by Edmund James Flynn.

title: 1900 Quebec general election


text:
User:Ggeudraco

Sometimes, fancy looking user pages just waste valuable time - so I don't bother :) Enjoy the encyclopædia and keep with the addition of new terms :)

Wiki-entries from ggeudraco:

title: User:Ggeudraco


text:
Setsubun

Setsubun (節分) is the day before the beginning of spring in the old calendar in Japan. The name literally means 'seasonal division', referring to the day just before the first day of spring in the traditional calendar, known as ; though previously referring to a wider range of possible dates, is now typically held on February 3 (in 2021 it was on 2nd February), with the day after – the first day of spring in the old calendar – known as Risshun (立春). Both and  are celebrated yearly as part of the Spring Festival (Haru matsuri (春祭)) in Japan. was accompanied by a number of rituals and traditions held at various levels to drive away the previous year's bad fortunes and evil spirits for the year to come.

History
has its origins in tsuina (追儺), a Chinese custom introduced to Japan in the 8th century. It was quite different from the known today. According to the Japanese history book, was first held in Japan in 706, and it was an event to ward off evil spirits held at the court on the last day of the year according to the lunar-solar calendar. At that time, was an event to drive away evil spirits that brought misfortune and disease by decorating each gate of the palace with clay figures of cows and children and using peach branches and walking sticks.

The custom of as we know it today began in the Muromachi period (1336–1573). Every household of the aristocracy and samurai class threw beans from their houses into the open air. The, a dictionary compiled during the Muromachi period, states that the practice of bean-throwing during originated from a legend in the 10th century, during the reign of Emperor Uda, that a monk on Mt. Kurama escaped misfortune by blinding  with roasted beans. The Japanese word for bean, 豆, is pronounced, which can be written as devil's eye (魔目), and some believe that the pronunciation is similar to that of mametsu (魔滅), meaning 'to destroy the devil', which is why people began throwing beans during.

From the Edo period (1603–1867), the custom of throwing beans at Shinto shrines, Buddhist temples, and homes of ordinary people spread throughout Japan as an event or festival to drive away evil spirits during. It was also during this period that the custom of tying roasted sardine heads to holly sprig to decorate the gates of houses during began. This custom was intended to scare away with the thorns of the holly leaves and the smell of the roasted sardines. The original form of this custom is recorded in the, compiled in 934 during the Heian period (794–1185). The diary describes a Shinto (sacred rope) that was hung on the gate of a house during the New Year's holiday to mark the boundary of purification, and that a mullet head pierced with a sprig of holly was attached to the.

The custom of eating ehōmaki (恵方巻) on began in the geisha districts from the Edo period to the Meiji period. is a special (sushi roll) eaten on. On, people face the most auspicious direction of the year and eat the whole , an uncut sushi roll, to pray for prosperity and happiness for the year. It is believed that it was originally called simply marukaburi zushi (丸かぶり寿司) or futomaki zushi (太巻き寿司). The name may have spread throughout Japan in 1989, when a Japanese convenience store chain renamed it  and began selling it.

The main ritual associated with the observance of is bean scattering (豆撒き); this ritual sees roasted soybeans (known as fortune beans (福豆)) either thrown out of the front door, or at a member of the family wearing an  (demon or ogre) mask while shouting Devils out! Fortune in! (鬼は外! 福は内!), before slamming the door. The beans are thought to symbolically purify the home by driving away the evil spirits that bring misfortune and bad health with them. Then, as part of bringing luck in, it is customary to eat roasted soybeans, one for each year of one's life, plus one more for bringing good luck for the year.

The custom of first appeared in the Muromachi period, and is usually performed by either a man of the household born in the corresponding zodiac year for the new year (toshiotoko (年男)), or else the male head of the household.

Because Watanabe no Tsuna, a retainer of Minamoto no Yorimitsu during the Heian period (794–1185), is associated with the legend that he vanquished historically considered to be the strongest, such as Shuten-doji and Ibaraki-doji, there is a tradition that  stay away from people named Watanabe and their houses. For this reason, some families with the surname Watanabe have not practiced the custom of throwing beans on Setsubun for generations. Watanabe no Tsuna was the first person to take the surname Watanabe, and Watanabe is the fifth most common surname in Japan, with approximately 1.08 million people.

Though still a somewhat common practice in households, many people will also or instead attend a shrine or temple's spring festival, where the practice of is performed; in some areas, such as Kyoto, this involves a dance performed by apprentice geisha, after which the apprentices themselves throw packets of roasted soybeans to the crowds. In other areas, priests and invited guests throw packets of roasted soybeans, some wrapped in gold or silver foil, small envelopes with money, sweets, candies and other prizes. In some bigger and more central shrines, celebrities and sumo wrestlers are invited to celebrations, usually to events that are televised. At Sensō-ji in the Asakusa neighborhood of Tokyo, crowds of nearly 100,000 people attend the annual festivities.

Other practices

A number of other, in some cases more esoteric practices exist surrounding the celebration and observance of ; some are regional, such as the Kansai area tradition of eating uncut rolls, known as lucky direction roll (恵方巻), in silence whilst facing the year's lucky compass direction as determined by the zodiac symbol of that year. Though the custom originated in Osaka, it has since spread, due largely to marketing efforts by grocery and convenience stores.

Other practices include the putting up of small decorations of sardine heads and holly leaves (柊鰯)) at the entrance to a house to ward off evil spirits. A special variety of sake known as shōgazake (生姜酒) brewed with ginger is also customarily drunk on . Each region of Japan has its own lucky charms to eat on . Soybeans used for and soba are the most common, but peanuts in the Hokkaido and Tōhoku region,  and  in the Kanto region, tea with kelp and sardines in Kansai region, konjac in Shikoku region, sea cucumber in the Oki Islands, and whale in the San'in region are also eaten.

Historical practices
The new year was felt to be a time when the spirit world became close to the physical world, thus the need to perform to drive away any wandering spirits that might happen too close to one's home. Other customs during this time included religious dances, festivals, and bringing tools inside the house that might normally be left outside, to prevent the spirits from harming them. Rice cakes were also balanced on lintels and windowsills.

Because is considered to be a day set apart from the rest of the year, a tradition of role reversal in appearance and dress was also practiced; such customs included girls wearing the hairstyles of older women and vice versa, wearing disguises, and cross-dressing. This custom is still practiced among geisha and their clients when entertaining on.

Traveling entertainers (旅芸人), who were normally shunned during the year because they were considered vagrants, were welcomed on to perform morality plays. Their vagrancy worked to their advantage in these cases, as they were considered to take evil spirits with them.

Regional variations
In the Tōhoku area of Japan, the head of the household (traditionally the father) would take roasted beans in his hand, pray at the family shrine, and then toss the sanctified beans out the door. Peanuts (either raw or coated in a sweet, crunchy batter) are sometimes used in place of soybeans.

There are many variations on the famous chant. For example, in the city of Aizuwakamatsu, people chant Blind the demons' eyes! (鬼の目玉ぶっつぶせ！)

title: Setsubun