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<H1>DSVectors</H1>
Compute vectors associated to the dense system such as eigenvectors.
<H3><FONT COLOR="#883300">Synopsis</FONT></H3>
<PRE>
#include "slepcds.h"
<A HREF="https://petsc.org/release/manualpages/Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../DS/DSVectors.html#DSVectors">DSVectors</A>(<A HREF="../DS/DS.html#DS">DS</A> ds,<A HREF="../DS/DSMatType.html#DSMatType">DSMatType</A> mat,<A HREF="https://petsc.org/release/manualpages/Sys/PetscInt.html#PetscInt">PetscInt</A> *j,<A HREF="https://petsc.org/release/manualpages/Sys/PetscReal.html#PetscReal">PetscReal</A> *rnorm)
</PRE>
Logically Collective
<P>
<H3><FONT COLOR="#883300">Input Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>ds </B></TD><TD> - the direct solver context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>mat </B></TD><TD> - the matrix, used to indicate which vectors are required
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Input/Output Parameter</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>j </B></TD><TD> - (optional) index of vector to be computed
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Output Parameter</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>rnorm </B></TD><TD> - (optional) computed residual norm
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Notes</FONT></H3>
Allowed values for mat are <A HREF="../DS/DSMatType.html#DSMatType">DS_MAT_X</A>, <A HREF="../DS/DSMatType.html#DSMatType">DS_MAT_Y</A>, <A HREF="../DS/DSMatType.html#DSMatType">DS_MAT_U</A> and <A HREF="../DS/DSMatType.html#DSMatType">DS_MAT_V</A>, to
compute right or left eigenvectors, or left or right singular vectors,
respectively.
<P>
If NULL is passed in argument j then all vectors are computed,
otherwise j indicates which vector must be computed. In real non-symmetric
problems, on exit the index j will be incremented when a complex conjugate
pair is found.
<P>
This function can be invoked after the dense problem has been solved,
to get the residual norm estimate of the associated Ritz pair. In that
case, the relevant information is returned in rnorm.
<P>
For computing eigenvectors, LAPACK's _trevc is used so the matrix must
be in (quasi-)triangular form, or call <A HREF="../DS/DSSolve.html#DSSolve">DSSolve</A>() first.
<P>
<P>
<H3><FONT COLOR="#883300">See Also</FONT></H3>
<A HREF="../DS/DSSolve.html#DSSolve">DSSolve</A>()
<BR><P><B></B><H3><FONT COLOR="#883300">Level</FONT></H3>intermediate<BR>
<H3><FONT COLOR="#883300">Location</FONT></H3>
</B><A HREF="../../../src/sys/classes/ds/interface/dsops.c.html#DSVectors">src/sys/classes/ds/interface/dsops.c</A>
<BR><BR><A HREF="./index.html">Index of all DS routines</A>
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