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<div class="ChapSects" ><a href="chap5_mj.html#X838651287FCCEFD8" >5 <span class="Heading" >Relations</span ></a>
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap5_mj.html#X87DADB7B7CB126DC" >5.1 <span class="Heading" >Relations: Categories and Representations</span ></a>
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<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5_mj.html#X80AD050F7999B7C0" >5.1-1 IsHomalgRelations</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5_mj.html#X790F68B17A4846DC" >5.1-2 IsHomalgRelationsOfLeftModule</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5_mj.html#X7FF5A3B180614698" >5.1-3 IsHomalgRelationsOfRightModule</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5_mj.html#X8322A26C84E80303" >5.1-4 IsRelationsOfFinitelyPresentedModuleRep</a></span >
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<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap5_mj.html#X7CF74FB785F90889" >5.2 <span class="Heading" >Relations: Constructors</span ></a>
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<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap5_mj.html#X859231317954D702" >5.3 <span class="Heading" >Relations: Properties</span ></a>
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<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5_mj.html#X798D893B7FBFCF07" >5.3-1 CanBeUsedToDecideZeroEffectively</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5_mj.html#X7B9398827AEEA2E6" >5.3-2 IsInjectivePresentation</a></span >
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<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap5_mj.html#X7EF7BBCA85851EF1" >5.4 <span class="Heading" >Relations: Attributes</span ></a>
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<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap5_mj.html#X7890B5EA80774AB5" >5.5 <span class="Heading" >Relations: Operations and Functions</span ></a>
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<h3>5 <span class="Heading" >Relations</span ></h3>
<p>A finite presentation of a module is given by a finite set of generators and a finite set of relations among these generators. In <strong class="pkg" >homalg</strong > a set of relations of a left/right module is given by a matrix <var class="Arg" >rel</var >, the rows/columns of which are interpreted as relations among <span class="SimpleMath" >\(n\)</span > generators, <span class="SimpleMath" >\(n\)</span > being the number of columns/rows of the matrix <var class="Arg" >rel</var >.</p>
<p>The data structure of a module in <strong class="pkg" >homalg</strong > is designed to contain not only one but several sets of relations (together with corresponding sets of generators (--> Chapter <a href="chap6_mj.html#X7BD5B55C802805B4" ><span class="RefLink" >6</span ></a>)). The different sets of relations are linked with so-called transition matrices (--> Chapter <a href="chap7_mj.html#X8183A6857B0C3633" ><span class="RefLink" >7</span ></a>).</p>
<p>The relations of a <strong class="pkg" >homalg</strong > module are evaluated in a lazy way. This avoids unnecessary computations.</p>
<p><a id="X87DADB7B7CB126DC" name="X87DADB7B7CB126DC" ></a></p>
<h4>5.1 <span class="Heading" >Relations: Categories and Representations</span ></h4>
<p><a id="X80AD050F7999B7C0" name="X80AD050F7999B7C0" ></a></p>
<h5>5.1-1 IsHomalgRelations</h5>
<div class="func" ><table class="func" width="100%" ><tr ><td class="tdleft" ><code class="func" >‣ IsHomalgRelations</code >( <var class="Arg" >rel</var > )</td ><td class="tdright" >( category )</td ></tr ></table ></div >
<p>Returns: <code class="code" >true</code > or <code class="code" >false</code ></p>
<p>The <strong class="pkg" >GAP</strong > category of <strong class="pkg" >homalg</strong > relations.</p>
<p><a id="X790F68B17A4846DC" name="X790F68B17A4846DC" ></a></p>
<h5>5.1-2 IsHomalgRelationsOfLeftModule</h5>
<div class="func" ><table class="func" width="100%" ><tr ><td class="tdleft" ><code class="func" >‣ IsHomalgRelationsOfLeftModule</code >( <var class="Arg" >rel</var > )</td ><td class="tdright" >( category )</td ></tr ></table ></div >
<p>Returns: <code class="code" >true</code > or <code class="code" >false</code ></p>
<p>The <strong class="pkg" >GAP</strong > category of <strong class="pkg" >homalg</strong > relations of a left module.</p>
<p>(It is a subcategory of the <strong class="pkg" >GAP</strong > category <code class="code" >IsHomalgRelations</code >.)</p>
<p><a id="X7FF5A3B180614698" name="X7FF5A3B180614698" ></a></p>
<h5>5.1-3 IsHomalgRelationsOfRightModule</h5>
<div class="func" ><table class="func" width="100%" ><tr ><td class="tdleft" ><code class="func" >‣ IsHomalgRelationsOfRightModule</code >( <var class="Arg" >rel</var > )</td ><td class="tdright" >( category )</td ></tr ></table ></div >
<p>Returns: <code class="code" >true</code > or <code class="code" >false</code ></p>
<p>The <strong class="pkg" >GAP</strong > category of <strong class="pkg" >homalg</strong > relations of a right module.</p>
<p>(It is a subcategory of the <strong class="pkg" >GAP</strong > category <code class="code" >IsHomalgRelations</code >.)</p>
<p><a id="X8322A26C84E80303" name="X8322A26C84E80303" ></a></p>
<h5>5.1-4 IsRelationsOfFinitelyPresentedModuleRep</h5>
<div class="func" ><table class="func" width="100%" ><tr ><td class="tdleft" ><code class="func" >‣ IsRelationsOfFinitelyPresentedModuleRep</code >( <var class="Arg" >rel</var > )</td ><td class="tdright" >( representation )</td ></tr ></table ></div >
<p>Returns: <code class="code" >true</code > or <code class="code" >false</code ></p>
<p>The <strong class="pkg" >GAP</strong > representation of a finite set of relations of a finitely presented <strong class="pkg" >homalg</strong > module.</p>
<p>(It is a representation of the <strong class="pkg" >GAP</strong > category <code class="func" >IsHomalgRelations</code > (<a href="chap5_mj.html#X80AD050F7999B7C0" ><span class="RefLink" >5.1-1</span ></a>))</p>
<p><a id="X7CF74FB785F90889" name="X7CF74FB785F90889" ></a></p>
<h4>5.2 <span class="Heading" >Relations: Constructors</span ></h4>
<p><a id="X859231317954D702" name="X859231317954D702" ></a></p>
<h4>5.3 <span class="Heading" >Relations: Properties</span ></h4>
<p><a id="X798D893B7FBFCF07" name="X798D893B7FBFCF07" ></a></p>
<h5>5.3-1 CanBeUsedToDecideZeroEffectively</h5>
<div class="func" ><table class="func" width="100%" ><tr ><td class="tdleft" ><code class="func" >‣ CanBeUsedToDecideZeroEffectively</code >( <var class="Arg" >rel</var > )</td ><td class="tdright" >( property )</td ></tr ></table ></div >
<p>Returns: <code class="code" >true</code > or <code class="code" >false</code ></p>
<p>Check if the <strong class="pkg" >homalg</strong > set of relations <var class="Arg" >rel</var > can be used for normal form reductions. <br /> (no method installed)</p>
<p><a id="X7B9398827AEEA2E6" name="X7B9398827AEEA2E6" ></a></p>
<h5>5.3-2 IsInjectivePresentation</h5>
<div class="func" ><table class="func" width="100%" ><tr ><td class="tdleft" ><code class="func" >‣ IsInjectivePresentation</code >( <var class="Arg" >rel</var > )</td ><td class="tdright" >( property )</td ></tr ></table ></div >
<p>Returns: <code class="code" >true</code > or <code class="code" >false</code ></p>
<p>Check if the <strong class="pkg" >homalg</strong > set of relations <var class="Arg" >rel</var > has zero syzygies.</p>
<p><a id="X7EF7BBCA85851EF1" name="X7EF7BBCA85851EF1" ></a></p>
<h4>5.4 <span class="Heading" >Relations: Attributes</span ></h4>
<p><a id="X7890B5EA80774AB5" name="X7890B5EA80774AB5" ></a></p>
<h4>5.5 <span class="Heading" >Relations: Operations and Functions</span ></h4>
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