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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" xmlns:scilab="http://www.scilab.org" xml:lang="en" xml:id="svd">
    <refnamediv>
        <refname>svd</refname>
        <refpurpose>singular value decomposition</refpurpose>
    </refnamediv>
    <refsynopsisdiv>
        <title>Syntax</title>
        <synopsis>s=svd(X)
            [U,S,V]=svd(X)
            [U,S,V]=svd(X,0) (obsolete)
            [U,S,V]=svd(X,"e")
            [U,S,V,rk]=svd(X [,tol])
        </synopsis>
    </refsynopsisdiv>
    <refsection>
        <title>Arguments</title>
        <variablelist>
            <varlistentry>
                <term>X</term>
                <listitem>
                    <para>a real or complex matrix</para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>s</term>
                <listitem>
                    <para>real vector (singular values)</para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>S</term>
                <listitem>
                    <para>real diagonal matrix (singular values)</para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>U,V</term>
                <listitem>
                    <para>orthogonal or unitary square matrices (singular vectors).</para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>tol</term>
                <listitem>
                    <para>real number</para>
                </listitem>
            </varlistentry>
        </variablelist>
    </refsection>
    <refsection>
        <title>Description</title>
        <para>
            <literal>[U,S,V] = svd(X)</literal> produces a diagonal matrix
            <literal>S</literal> , of the same dimension as <literal>X</literal> and with
            nonnegative diagonal elements in decreasing order, and unitary
            matrices <literal>U</literal> and <literal>V</literal> so that <literal>X = U*S*V'</literal>.
        </para>
        <para>
            <literal>[U,S,V] = svd(X,0)</literal> produces the "economy
            size" decomposition. If <literal>X</literal> is m-by-n with m &gt;
            n, then only the first n columns of <literal>U</literal> are computed
            and <literal>S</literal> is n-by-n.
        </para>
        <para>
            <literal>s= svd(X)</literal> by itself, returns a vector <literal>s</literal>
            containing the singular values.
        </para>
        <para>
            <literal>[U,S,V,rk]=svd(X,tol)</literal> gives in addition <literal>rk</literal>, the numerical rank of <literal>X</literal> i.e. the number of
            singular values larger than <literal>tol</literal>.
        </para>
        <para>
            The default value of <literal>tol</literal> is the same as in <literal>rank</literal>.
        </para>
    </refsection>
    <refsection>
        <title>Examples</title>
        <programlisting role="example"><![CDATA[
X=rand(4,2)*rand(2,4)
svd(X)
sqrt(spec(X*X'))
 ]]></programlisting>
    </refsection>
    <refsection role="see also">
        <title>See also</title>
        <simplelist type="inline">
            <member>
                <link linkend="rank">rank</link>
            </member>
            <member>
                <link linkend="qr">qr</link>
            </member>
            <member>
                <link linkend="colcomp">colcomp</link>
            </member>
            <member>
                <link linkend="rowcomp">rowcomp</link>
            </member>
            <member>
                <link linkend="sva">sva</link>
            </member>
            <member>
                <link linkend="spec">spec</link>
            </member>
        </simplelist>
    </refsection>
    <refsection>
        <title>Used Functions</title>
        <para>
            svd decompositions are based on  the Lapack routines DGESVD for
            real matrices and  ZGESVD for the complex case.
        </para>
    </refsection>
</refentry>
