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{{Built-in|Roll|?}} is a [[monadic]] [[scalar function]] which returns random or pseudo-random numbers. The name ''Roll'' comes from the analogy of rolling dice. Each [[scalar]] in the argument must be a positive integer, <source lang=apl inline>n</source>, and Roll chooses one of the first <source lang=apl inline>n</source> [[Index|indices]]. Some dialects allow <source lang=apl inline>n</source> to be zero, in which case Roll chooses a floating-point number between 0 and 1.
{{Built-in|Roll|?}} is a [[monadic]] [[scalar function]] which returns random or pseudo-random numbers. The name ''Roll'' comes from the analogy of rolling dice. Each [[scalar]] in the argument must be a positive integer, <source lang=apl inline>n</source>, and Roll chooses one of the first <source lang=apl inline>n</source> [[Index|indices]]. Some dialects allow <source lang=apl inline>n</source> to be zero, in which case Roll chooses a floating-point number between 0 and 1. Roll shares its [[glyph]] with the other random-result function, [[Deal]].


== Examples ==
== Examples ==
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Because [[Iota]] depends on [[index origin]], Roll depends on index origin unless every number in the argument is 0.
Because [[Iota]] depends on [[index origin]], Roll depends on index origin unless every number in the argument is 0.


The choices made by Roll do not have to be truly random: they may be pseudorandom (generated by a deterministic but difficult to predict algorithm) or taken from the operating system. They way random numbers are generated is controlled by the [[random link]] <source lang=apl inline>⎕RL</source>.
The choices made by Roll do not have to be truly random: they may be pseudorandom (generated by a deterministic but difficult to predict algorithm) or taken from the operating system. They way random numbers are generated is controlled by the [[random link]] <source lang=apl inline>⎕RL</source>. Traditionally, APL uses the [[wikipedia:Lehmer random number generator|Lehmer random number generator]], but [[Dyalog APL]] defaults to the allow choosing a different random number generator and defaults to the [[wikipedia:Mersenne Twister|Mersenne Twister]].


== External links ==
== External links ==
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=== Documentation ===
=== Documentation ===


* [http://help.dyalog.com/latest/index.htm#Language/Primitive%20Functions/Roll.htm Dyalog]
* [https://help.dyalog.com/latest/index.htm#Language/Primitive%20Functions/Roll.htm Dyalog]


* [http://microapl.com/apl_help/ch_020_020_170.htm APLX]
* [http://microapl.com/apl_help/ch_020_020_170.htm APLX]


* [https://www.jsoftware.com/help/dictionary/d640.htm J Dictionary], [https://code.jsoftware.com/wiki/Vocabulary/query J NuVoc]
* [https://www.jsoftware.com/help/dictionary/d640.htm J Dictionary], [https://code.jsoftware.com/wiki/Vocabulary/query J NuVoc]
{{APL built-ins}}
{{APL built-ins}}[[Category:Primitive functions]][[Category:Scalar monadic functions]]

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