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<?xml version="1.0" encoding="UTF-8"?>
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<refentry xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:svg="http://www.w3.org/2000/svg" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:db="http://docbook.org/ns/docbook" version="5.0-subset Scilab" xml:lang="en" xml:id="condestsp">
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<refname>condestsp</refname>
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<refpurpose> estimate the condition number of a sparse matrix </refpurpose>
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<title>Calling Sequence</title>
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<synopsis>[K1] = condestsp(A, LUp, t)
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[K1] = condestsp(A, LUp)
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[K1] = condestsp(A, t)
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<title>Arguments</title>
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<para>a real or complex square sparse matrix</para>
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<para>(optional) a pointer to (umf) LU factors of A obtained by a call to umf_lufact ;
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if you have already computed the LU (= PAQ) factors it is recommended to give
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this optional parameter (as the factorization may be time consuming)
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<para>(optional) a positive integer (default value 2) by increasing this one
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you may hope to get a better (even exact) estimate
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<para>estimated 1-norm condition number of A </para>
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<title>Description</title>
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Give an estimate of the 1-norm condition number of
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the sparse matrix A by Algorithm 2.4 appearing in :
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<programlisting role=""><![CDATA[
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<refname>condestsp</refname>
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<refpurpose> estimate the condition number of a sparse matrix </refpurpose>
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<title>Calling Sequence</title>
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<synopsis>[K1] = condestsp(A, LUp, t)
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[K1] = condestsp(A, LUp)
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[K1] = condestsp(A, t)
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<title>Arguments</title>
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<para>a real or complex square sparse matrix</para>
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<para>(optional) a pointer to (umf) LU factors of A obtained by a call to umf_lufact ;
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if you have already computed the LU (= PAQ) factors it is recommended to give
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this optional parameter (as the factorization may be time consuming)
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<para>(optional) a positive integer (default value 2) by increasing this one
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you may hope to get a better (even exact) estimate
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<para>estimated 1-norm condition number of A </para>
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<title>Description</title>
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Give an estimate of the 1-norm condition number of
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the sparse matrix A by Algorithm 2.4 appearing in :
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<programlisting role=""><![CDATA[
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"A block algorithm for matrix 1-norm estimation
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with an application to 1-norm pseudospectra"
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Nicholas J. Higham and Francoise Tisseur
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Siam J. Matrix Anal. Appl., vol 21, No 4, pp 1185-1201
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]]></programlisting>
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Noting the exact condition number <literal>K1e = ||A||_1 ||A^(-1)||_1</literal>,
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we have always <literal>K1 <= K1e</literal> and this estimate gives in most case
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something superior to <literal>1/2 K1e</literal>
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<title>Examples</title>
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<programlisting role="example"><![CDATA[
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Noting the exact condition number <literal>K1e = ||A||_1 ||A^(-1)||_1</literal>,
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we have always <literal>K1 <= K1e</literal> and this estimate gives in most case
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something superior to <literal>1/2 K1e</literal>
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<title>Examples</title>
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<programlisting role="example"><![CDATA[
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A = sparse( [ 2 3 0 0 0;
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K1 = condestsp(A,Lup)
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umf_ludel(Lup) // clear memory
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]]></programlisting>
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<refsection role="see also">
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<title>See Also</title>
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<simplelist type="inline">
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<link linkend="umf_lufact">umf_lufact</link>
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<link linkend="rcond">rcond</link>
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<refsection role="see also">
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<title>See Also</title>
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<simplelist type="inline">
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<link linkend="umf_lufact">umf_lufact</link>
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<link linkend="rcond">rcond</link>