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<div id="version" align=right><b>slepc-3.22.2 2024-12-02</b></div>
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<H1>STSetPreconditionerMat</H1>
Sets the matrix to be used to build the preconditioner.
<H3><FONT COLOR="#883300">Synopsis</FONT></H3>
<PRE>
#include "slepcst.h"
<A HREF="https://petsc.org/release/manualpages/Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../ST/STSetPreconditionerMat.html#STSetPreconditionerMat">STSetPreconditionerMat</A>(<A HREF="../ST/ST.html#ST">ST</A> st,<A HREF="https://petsc.org/release/manualpages/Mat/Mat.html#Mat">Mat</A> mat)
</PRE>
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>st </B></TD><TD> - the spectral transformation context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>mat </B></TD><TD> - the matrix that will be used in constructing the preconditioner
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Notes</FONT></H3>
This matrix will be passed to the internal <A HREF="https://petsc.org/release/manualpages/KSP/KSP.html#KSP">KSP</A> object (via the last argument
of <A HREF="https://petsc.org/release/manualpages/KSP/KSPSetOperators.html#KSPSetOperators">KSPSetOperators</A>()) as the matrix to be used when constructing the preconditioner.
If no matrix is set or mat is set to NULL, A-sigma*B will be used
to build the preconditioner, being sigma the value set by <A HREF="../ST/STSetShift.html#STSetShift">STSetShift</A>().
<P>
More precisely, this is relevant for spectral transformations that represent
a rational matrix function, and use a <A HREF="https://petsc.org/release/manualpages/KSP/KSP.html#KSP">KSP</A> object for the denominator, called
K in the description of <A HREF="../ST/STGetOperator.html#STGetOperator">STGetOperator</A>(). It includes also the STPRECOND case.
If the user has a good approximation to matrix K that can be used to build a
cheap preconditioner, it can be passed with this function. Note that it affects
only the Pmat argument of <A HREF="https://petsc.org/release/manualpages/KSP/KSPSetOperators.html#KSPSetOperators">KSPSetOperators</A>(), not the Amat argument.
<P>
If a preconditioner matrix is set, the default is to use an iterative <A HREF="https://petsc.org/release/manualpages/KSP/KSP.html#KSP">KSP</A>
rather than a direct method.
<P>
An alternative to pass an approximation of A-sigma*B with this function is
to provide approximations of A and B via <A HREF="../ST/STSetSplitPreconditioner.html#STSetSplitPreconditioner">STSetSplitPreconditioner</A>(). The
difference is that when sigma changes the preconditioner is recomputed.
<P>
Use NULL to remove a previously set matrix.
<P>
<P>
<H3><FONT COLOR="#883300">See Also</FONT></H3>
<A HREF="../ST/STGetPreconditionerMat.html#STGetPreconditionerMat">STGetPreconditionerMat</A>(), <A HREF="../ST/STSetShift.html#STSetShift">STSetShift</A>(), <A HREF="../ST/STGetOperator.html#STGetOperator">STGetOperator</A>(), <A HREF="../ST/STSetSplitPreconditioner.html#STSetSplitPreconditioner">STSetSplitPreconditioner</A>()
<BR><P><B></B><H3><FONT COLOR="#883300">Level</FONT></H3>advanced<BR>
<H3><FONT COLOR="#883300">Location</FONT></H3>
</B><A HREF="../../../src/sys/classes/st/interface/stfunc.c.html#STSetPreconditionerMat">src/sys/classes/st/interface/stfunc.c</A>
<P><H3><FONT COLOR="#883300">Examples</FONT></H3>
<A HREF="../../../src/eps/tutorials/ex24.c.html">src/eps/tutorials/ex24.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex34.c.html">src/eps/tutorials/ex34.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex46.c.html">src/eps/tutorials/ex46.c</A><BR>
<BR><BR><A HREF="./index.html">Index of all ST routines</A>
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