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<H1>STSetMatMode</H1>
Sets a flag to indicate how the matrix is being shifted in the shift-and-invert and Cayley spectral transformations.
<H3><FONT COLOR="#883300">Synopsis</FONT></H3>
<PRE>
#include "slepcst.h"
PetscErrorCode STSetMatMode(ST st,STMatMode mode)
</PRE>
Logically Collective on <A HREF="../ST/ST.html#ST">ST</A>
<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>st </B></TD><TD> - the spectral transformation context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>mode </B></TD><TD> - the mode flag, one of ST_MATMODE_COPY,
ST_MATMODE_INPLACE or ST_MATMODE_SHELL
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Options Database Key</FONT></H3>
<DT><B>-st_matmode <mode> </B> - Indicates the mode flag, where <mode> is one of
'copy', 'inplace' or 'shell' (see explanation below).
<br>
<P>
<H3><FONT COLOR="#883300">Notes</FONT></H3>
By default (ST_MATMODE_COPY), a copy of matrix A is made and then
this copy is shifted explicitly, e.g. A <- (A - s B).
<P>
With ST_MATMODE_INPLACE, the original matrix A is shifted at
<A HREF="../ST/STSetUp.html#STSetUp">STSetUp</A>() and unshifted at the end of the computations. With respect to
the previous one, this mode avoids a copy of matrix A. However, a
backdraw is that the recovered matrix might be slightly different
from the original one (due to roundoff).
<P>
With ST_MATMODE_SHELL, the solver works with an implicit shell
matrix that represents the shifted matrix. This mode is the most efficient
in creating the shifted matrix but it places serious limitations to the
linear solves performed in each iteration of the eigensolver (typically,
only interative solvers with Jacobi preconditioning can be used).
<P>
In the case of generalized problems, in the two first modes the matrix
A - s B has to be computed explicitly. The efficiency of this computation
can be controlled with <A HREF="../ST/STSetMatStructure.html#STSetMatStructure">STSetMatStructure</A>().
<P>
<P>
<H3><FONT COLOR="#883300">See Also</FONT></H3>
<A HREF="../ST/STSetOperators.html#STSetOperators">STSetOperators</A>(), <A HREF="../ST/STSetMatStructure.html#STSetMatStructure">STSetMatStructure</A>(), <A HREF="../ST/STGetMatMode.html#STGetMatMode">STGetMatMode</A>(), <A HREF="../ST/STMatMode.html#STMatMode">STMatMode</A>
<BR><P><B><FONT COLOR="#883300">Location: </FONT></B><A HREF="../../../src/st/interface/stset.c.html#STSetMatMode">src/st/interface/stset.c</A>
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