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<!-- %A  integers.msk                GAP documentation            Martin Schönert -->
<!-- %A                                                           Alexander Hulpke -->
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<!-- %A  @(#)<M>Id: integers.msk,v 1.26 2006/08/22 09:55:00 gap Exp </M> -->
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<!-- %Y  (C) 1998 School Math and Comp. Sci., University of St Andrews, Scotland -->
<!-- %Y  Copyright (C) 2002 The GAP Group -->
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<Chapter Label="Integers">
<Heading>Integers</Heading>

One of the most fundamental datatypes in every programming language is
the integer type.  &GAP; is no exception.
<P/>
&GAP; integers are entered as a sequence of decimal digits optionally 
preceded by a <Q><C>+</C></Q> sign for positive integers or 
a <Q><C>-</C></Q> sign for negative integers.
The size of integers in &GAP; is only limited by the amount of available
memory, so you can compute with integers having thousands of digits.
<P/>
<Example><![CDATA[
gap> -1234;
-1234
gap> 123456789012345678901234567890123456789012345678901234567890;
123456789012345678901234567890123456789012345678901234567890
]]></Example>
<P/>

Many more functions that are mainly related to the prime residue group of
integers modulo an integer are described in chapter&nbsp;<Ref Chap="Number Theory"/>,
and functions dealing with combinatorics can be found
in chapter&nbsp;<Ref Chap="Combinatorics"/>.


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<Section Label="sect:Integers: Global Variables">
<Heading>Integers: Global Variables</Heading>

<#Include Label="IntegersGlobalVars">
<#Include Label="IsIntegers">

</Section>


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<Section Label="Elementary Operations for Integers">
<Heading>Elementary Operations for Integers</Heading>

<#Include Label="IsInt">
<#Include Label="IsPosInt">
<#Include Label="Int">
<#Include Label="IsEvenInt">
<#Include Label="IsOddInt">
<#Include Label="AbsInt">
<#Include Label="SignInt">
<#Include Label="LogInt">
<#Include Label="RootInt">
<#Include Label="SmallestRootInt">
<#Include Label="ListOfDigits">

<ManSection>
<Meth Name="Random" Arg='Integers' Label="for integers"/>

<Description>
<Ref Meth="Random" Label="for integers"/> for integers returns
pseudo random integers between <M>-10</M> and
<M>10</M> distributed according to a binomial distribution.
To generate uniformly distributed integers from a range,
use the construction <C>Random( [ <A>low</A> .. <A>high</A> ] )</C>
&nbsp;(see&nbsp;<Ref Meth="Random" Label="for lower and upper bound"/>).
</Description>
</ManSection>

</Section>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Section Label="Quotients and Remainders">
<Heading>Quotients and Remainders</Heading>

<#Include Label="QuoInt">
<#Include Label="BestQuoInt">
<#Include Label="RemInt">
<#Include Label="GcdInt">
<#Include Label="Gcdex">
<#Include Label="LcmInt">
<#Include Label="CoefficientsQadic">
<#Include Label="CoefficientsMultiadic">
<#Include Label="ChineseRem">
<#Include Label="PowerModInt">

</Section>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Section Label="Prime Integers and Factorization">
<Heading>Prime Integers and Factorization</Heading>

<#Include Label="Primes">
<#Include Label="IsPrimeInt">
<#Include Label="PrimalityProof">
<#Include Label="IsPrimePowerInt">
<#Include Label="NextPrimeInt">
<#Include Label="PrevPrimeInt">
<#Include Label="FactorsInt">
<#Include Label="PrimeDivisors">
<#Include Label="PartialFactorization">
<#Include Label="PrintFactorsInt">
<#Include Label="PrimePowersInt">
<#Include Label="DivisorsInt">

</Section>


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<Section Label="Residue Class Rings">
<Heading>Residue Class Rings</Heading>

<Index Key="mod" Subkey="residue class rings"><K>mod</K></Index>
<Index Subkey="residue class rings">modulo</Index>
<Ref Func="ZmodnZ"/> returns a residue class ring of <Ref Var="Integers"/>
modulo an ideal.
These residue class rings are rings, thus all operations for rings
(see Chapter&nbsp;<Ref Chap="Rings"/>) apply.
See also Chapters&nbsp;<Ref Chap="Finite Fields"/> and
<Ref Chap="Number Theory"/>.

<ManSection>
<Oper Name="\mod" Arg="r/s, n" Label="for residue class rings"/>
<Description>
If <A>r</A>, <A>s</A> and <A>n</A> are integers, <C><A>r</A> / <A>s</A></C> as a  reduced  fraction  is
<C>p/q</C>, where <C>q</C> and <A>n</A> are coprime, then <C><A>r</A> / <A>s</A> mod <A>n</A></C>  is
defined to be the product of <C>p</C> and the inverse of <C>q</C> modulo  <A>n</A>. See
Section&nbsp;<Ref Sect="Arithmetic Operators"/> for more details and definitions.
<P/>
With the above definition, <C>4 / 6 mod 32</C> equals <C>2 / 3 mod 32</C> and hence
exists (and is equal to 22), despite the  fact  that  6  has  no  inverse
modulo 32.
</Description>
</ManSection>

<#Include Label="ZmodnZ">
<#Include Label="ZmodnZObj">
<#Include Label="IsZmodnZObj">

</Section>

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<Section Label="Check Digits">
<Heading>Check Digits</Heading>

<#Include Label="CheckDigitISBN">
<#Include Label="CheckDigitTestFunction">

</Section>


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<Section Label="Random Sources">
<Heading>Random Sources</Heading>

&GAP; provides <Ref Func="Random" Label="for a list or collection"/> methods
for many collections of objects. 
On a lower level these methods use <E>random sources</E> which provide 
random integers and random choices from lists. 

<#Include Label="IsRandomSource">
<#Include Label="Random">
<#Include Label="State">
<#Include Label="IsGlobalRandomSource">
<#Include Label="RandomSource">

</Section>
</Chapter>