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<?xml version="1.0" encoding="UTF-8"?>
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* Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
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* Copyright (C) 2008 - INRIA
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* This file must be used under the terms of the CeCILL.
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* This source file is licensed as described in the file COPYING, which
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* you should have received as part of this distribution. The terms
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* are also available at
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* http://www.cecill.info/licences/Licence_CeCILL_V2-en.txt
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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="psmall">
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<refname>psmall</refname>
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<refpurpose> spectral projection</refpurpose>
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<title>Calling Sequence</title>
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<synopsis>[Q,M]=psmall(A,thres,flag)</synopsis>
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<title>Arguments</title>
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<para>real square matrix</para>
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<para>real number</para>
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character string (<literal>'c'</literal> or <literal>'d'</literal>)
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<para>real matrices</para>
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<title>Description</title>
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Projection on eigen-subspace associated with eigenvalues with real
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part < <literal>thres</literal> (<literal>flag='c'</literal>) or
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with modulus < <literal>thres</literal>
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(<literal>flag='d'</literal>).
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The projection is defined by <literal>Q*M</literal>, <literal>Q</literal> is
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full column rank, <literal>M</literal> is full row rank and
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<literal>M*Q=eye</literal>.
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If <literal>flag='c'</literal>, the eigenvalues of
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<literal>M*A*Q</literal> = eigenvalues of <literal>A</literal> with real part
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< <literal>thres</literal>.
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If <literal>flag='d'</literal>, the eigenvalues of
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<literal>M*A*Q</literal> = eigenvalues of <literal>A</literal> with magnitude
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< <literal>thres</literal>.
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If <literal>flag='c'</literal> and if <literal>[Q1,M1]</literal> =
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full rank factorization (<literal>fullrf</literal>) of
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<literal>eye()-Q*M</literal> then eigenvalues of <literal>M1*A*Q1</literal> =
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eigenvalues of <literal>A</literal> with real part >=
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<literal>thres</literal>.
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If <literal>flag='d'</literal> and if <literal>[Q1,M1]</literal> =
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full rank factorization (<literal>fullrf</literal>) of
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<literal>eye()-Q*M</literal> then eigenvalues of <literal>M1*A*Q1</literal> =
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eigenvalues of <literal>A</literal> with magnitude >=
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<literal>thres</literal>.
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<title>Examples</title>
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<programlisting role="example"><![CDATA[
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A=diag([1,2,3]);X=rand(A);A=inv(X)*A*X;
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[Q,M]=psmall(A,2.5,'d');
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[Q1,M1]=fullrf(eye()-Q*M);
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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="pbig">pbig</link>
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<link linkend="proj">proj</link>
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<link linkend="projspec">projspec</link>
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<title>Used Functions</title>
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This function is based on the ordered schur form (scilab
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function <literal>schur</literal>).