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<div><h1>submatrix(Matrix,VisibleList) -- select columns</h1>
<div class="single"><h2>Synopsis</h2>
<ul><li><div class="list"><dl class="element"><dt class="heading">Usage: </dt><dd class="value"><div><tt>submatrix(f, cols)</tt></div>
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<li><span>Function: <a href="_submatrix.html" title="">submatrix</a></span></li>
<li><div class="single">Inputs:<ul><li><span><tt>f</tt>, <span>a <a href="___Matrix.html">matrix</a></span>, a map between free modules</span></li>
<li><span><tt>cols</tt>, <span>a <a href="___Visible__List.html">visible list</a></span>, a list of integers denoting the choice of columns</span></li>
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<li><div class="single">Outputs:<ul><li><span><span>a <a href="___Matrix.html">matrix</a></span>, the submatrix of <tt>f</tt> corresponding to the columns <tt>cols</tt></span></li>
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<div class="single"><h2>Description</h2>
<div>Yields an r by c matrix, where r is the number of rows of <tt>f</tt>, and c is the length of the list of integers <tt>cols</tt>. The <tt>(i,j)</tt>-th entry of the result is <tt>f_(i, cols_j)</tt>.<p/>
The list of integers, <tt>cols</tt>, may contain ranges and repetitions, as in <tt>{3, 5..7, 3:0}</tt><p/>
If the list of column indices is a permutation of 0 .. n-1, where n is the number of columns, then the result is the corresponding permutation of the columns of f.<table class="examples"><tr><td><pre>i1 : R = ZZ/101[a .. o];</pre>
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<tr><td><pre>i2 : f = genericMatrix(R, a, 3, 5)
o2 = | a d g j m |
| b e h k n |
| c f i l o |
3 5
o2 : Matrix R <--- R</pre>
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<tr><td><pre>i3 : submatrix(f, {1..3,0})
o3 = | d g j a |
| e h k b |
| f i l c |
3 4
o3 : Matrix R <--- R</pre>
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<div class="single"><h2>See also</h2>
<ul><li><span><a href="_submatrix_sq.html" title="exclude rows and/or columns of a matrix">submatrix'</a> -- exclude rows and/or columns of a matrix</span></li>
<li><span><a href="___Matrix_sp_us_sp__List.html" title="select columns">Matrix _ List</a> -- select columns</span></li>
<li><span><a href="___Matrix_sp^_sp__List.html" title="select rows">Matrix ^ List</a> -- select rows</span></li>
<li><span><a href="___Matrix_sp_us_sp__Array.html" title="component of map corresponding to summand of source">Matrix _ Array</a> -- component of map corresponding to summand of source</span></li>
<li><span><a href="___Matrix_sp^_sp__Array.html" title="component of map corresponding to summand of target">Matrix ^ Array</a> -- component of map corresponding to summand of target</span></li>
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