<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ HomalgFieldOfRationals</code>( )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a <strong class="pkg">homalg</strong> ring</p>
<p>The field of rationals <span class="SimpleMath">ℚ</span> is returned. The operation <code class="code">SetRingProperties</code> is automatically invoked to set the ring properties.</p>
<p>Please note that there are more tool functions you can define, <strong class="pkg">GaussForHomalg</strong> just provides homalg with a sufficient subset. This varies with the type and complexity of the rings you want to define. On the other hand, <code class="func">ImportMatrix</code> (<a href="chap3.html#X7B5E86C283147027"><span class="RefLink">3.2-4</span></a>) is a function specifically designed for <strong class="pkg">GaussForHomalg</strong>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IdentityMatrix</code>( <var class="Arg">C</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns a sparse <span class="SimpleMath">n × n</span> identity matrix with the same ring as the <strong class="pkg">homalg</strong> matrix <var class="Arg">C</var>, <span class="SimpleMath">n</span> being the number of rows of <var class="Arg">C</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ CopyMatrix</code>( <var class="Arg">C</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns a sparse matrix which is a shallow copy of the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">C</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ ImportMatrix</code>( <var class="Arg">M</var>, <var class="Arg">R</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns the sparse version of the <strong class="pkg">GAP</strong> matrix <var class="Arg">M</var> over the ring <var class="Arg">R</var>. It prevents <strong class="pkg">homalg</strong> from calling sparse matrix algorithms on dense <strong class="pkg">GAP</strong> matrices. Note that this is not a "standard" tool but neccessary because of the new data type.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Involution</code>( <var class="Arg">M</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns a sparse matrix which is the transpose of the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">M</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ CertainRows</code>( <var class="Arg">M</var>, <var class="Arg">plist</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns the rows in <var class="Arg">plist</var> of the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">M</var> as a new matrix.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ CertainColumns</code>( <var class="Arg">M</var>, <var class="Arg">plist</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns the columns in <var class="Arg">plist</var> of the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">M</var> as a new matrix.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ UnionOfRows</code>( <var class="Arg">L</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns the sparse matrix created by concatenating the rows of the sparse matrices stored in the <code class="code">Eval</code> attributes of the <strong class="pkg">homalg</strong> matrices in the list <var class="Arg">L</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ UnionOfColumns</code>( <var class="Arg">L</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns the sparse matrix created by concatenating the columns of the sparse matrices stored in the <code class="code">Eval</code> attributes of the <strong class="pkg">homalg</strong> matrices in the list <var class="Arg">L</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DiagMat</code>( <var class="Arg">e</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This method takes a list <var class="Arg">e</var> of <strong class="pkg">homalg</strong> matrices and returns the sparse block matrix of the matrices stored in the <code class="code">Eval</code> attributes of the matrices in <var class="Arg">e</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ KroneckerMat</code>( <var class="Arg">A</var>, <var class="Arg">B</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns the sparse Kronecker matrix of the matrices stored in the <code class="code">Eval</code> attributes of the <strong class="pkg">homalg</strong> matrices <var class="Arg">A</var> and <var class="Arg">B</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DualKroneckerMat</code>( <var class="Arg">A</var>, <var class="Arg">B</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns the sparse dual Kronecker matrix of the matrices stored in the <code class="code">Eval</code> attributes of the <strong class="pkg">homalg</strong> matrices <var class="Arg">A</var> and <var class="Arg">B</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Compose</code>( <var class="Arg">A</var>, <var class="Arg">B</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a sparse matrix</p>
<p>This returns the matrix product of the sparse matrices stored in the <code class="code">Eval</code> attributes of the <strong class="pkg">homalg</strong> matrices <var class="Arg">A</var> and <varclass="Arg">B</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ NumberRows</code>( <var class="Arg">C</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: an integer</p>
<p>This returns the number of rows of the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">C</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ NumberColumns</code>( <var class="Arg">C</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: an integer</p>
<p>This returns the number of columns of the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">C</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IsZeroMatrix</code>( <var class="Arg">C</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: <strong class="button">true</strong> or <strong class="button">false</strong></p>
<p>This returns <strong class="button">true</strong> if the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">C</var> is a zero matrix, and <strong class="button">false</strong> otherwise.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IsDiagonalMatrix</code>( <var class="Arg">C</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: <strong class="button">true</strong> or <strong class="button">false</strong></p>
<p>This returns <strong class="button">true</strong> if the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">C</var> is a diagonal matrix, and <strong class="button">false</strong> otherwise.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ ZeroRows</code>( <var class="Arg">C</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a list</p>
<p>This returns the list of zero rows of the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">C</var>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ ZeroColumns</code>( <var class="Arg">C</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a list</p>
<p>This returns the list of zero columns of the sparse matrix stored in the <code class="code">Eval</code> attribute of the <strong class="pkg">homalg</strong> matrix <var class="Arg">C</var>.</p>
<p>If one argument is given, this returns the triangular basis (reduced row echelon form) of the <strong class="pkg">homalg</strong> matrix <var class="Arg">M</var>, again as a <strong class="pkg">homalg</strong> matrix. In case of two arguments, still only the triangular basis of <var class="Arg">M</var> is returned, but the transformation matrix is stored in the void <strong class="pkg">homalg</strong> matrix <var class="Arg">U</var> as a side effect. The matrices satisfy <span class="SimpleMath">N = U * M</span>.</p>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ CreateHomalgTable</code>( <var class="Arg">R</var> )</td><td class="tdright">( function )</td></tr></table></div>
<p>Returns: a <strong class="pkg">homalg</strong> table</p>
<p>This returns the <strong class="pkg">homalg</strong> table of what will become the <strong class="pkg">homalg</strong> ring <var class="Arg">R</var> (at this point <var class="Arg">R</var> is just a <strong class="pkg">homalg</strong> object with some properties for the method selection of <code class="code">CreateHomalgTable</code>). This method includes the needed functions stored in the global variables <code class="code">CommonHomalgTableForGaussTools</code> and <code class="code">CommonHomalgTableForGaussBasic</code>, and can add some more to the record that will become the <strong class="pkg">homalg</strong> table.</p>
<p>If the Eval attribute of the homalg matrix <var class="Arg">M</var> over the <strong class="pkg">homalg</strong> ring <var class="Arg">R</var> is sparse, this calls the corresponding <strong class="pkg">Gauss</strong> command <code class="code">GetEntry</code>.</p>
<p>If the Eval attribute of the homalg matrix <var class="Arg">M</var> over the <strong class="pkg">homalg</strong> ring <var class="Arg">R</var> is sparse, this calls the corresponding <strong class="pkg">Gauss</strong> command <code class="code">GetEntry</code>, to achieve <code class="code"><var class="Arg">M</var>[<var class="Arg">r</var>,<var class="Arg">c</var>]:=<var class="Arg">e</var></code>.</p>
<p>If the Eval attribute of the homalg matrix <var class="Arg">M</var> over the <strong class="pkg">homalg</strong> ring <var class="Arg">R</var> is sparse, this calls the corresponding <strong class="pkg">Gauss</strong> command <code class="code">AddToEntry</code>, to achieve <code class="code"><var class="Arg">M</var>[<var class="Arg">r</var>,<var class="Arg">c</var>] := <var class="Arg">M</var>[<var class="Arg">r</var>,<var class="Arg">c</var>] + <var class="Arg">e</var></code>.</p>
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