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<h4 class="subsection">21.3.2 Permutation Matrix Functions</h4>
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<p><em>inv</em> and <em>pinv</em> will invert a permutation matrix, preserving its
specialness. <em>det</em> can be applied to a permutation matrix, efficiently
calculating the sign of the permutation (which is equal to the determinant).
</p>
<p>A permutation matrix can also be returned from the built-in functions
<em>lu</em> and <em>qr</em>, if a pivoted factorization is requested.
</p>
<p>The <em>sparse</em> function will convert a permutation matrix efficiently to a
sparse matrix.
The <em>find</em> function will also work efficiently with a permutation matrix,
making it possible to conveniently obtain the permutation indices.
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