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<div id="version" align=right><b>slepc-3.22.2 2024-12-02</b></div>
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<H1>STGetOperator</H1>
Returns a shell matrix that represents the operator of the spectral transformation.
<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/STGetOperator.html#STGetOperator">STGetOperator</A>(<A HREF="../ST/ST.html#ST">ST</A> st,<A HREF="https://petsc.org/release/manualpages/Mat/Mat.html#Mat">Mat</A> *Op)
</PRE>
Collective
<P>
<H3><FONT COLOR="#883300">Input Parameter</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></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>Op </B></TD><TD> - operator matrix
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Notes</FONT></H3>
The operator is defined in linear eigenproblems only, not in polynomial ones,
so the call will fail if more than 2 matrices were passed in <A HREF="../ST/STSetMatrices.html#STSetMatrices">STSetMatrices</A>().
<P>
The returned shell matrix is essentially a wrapper to the <A HREF="../ST/STApply.html#STApply">STApply</A>() and
<A HREF="../ST/STApplyTranspose.html#STApplyTranspose">STApplyTranspose</A>() operations. The operator can often be expressed as
<P>
<pre>
Op = D*inv(K)*M*inv(D)
</pre>
<P>
where D is the balancing matrix, and M and K are two matrices corresponding
to the numerator and denominator for spectral transformations that represent
a rational matrix function. In the case of <A HREF="../ST/STSHELL.html#STSHELL">STSHELL</A>, the inner part inv(K)*M
is replaced by the user-provided operation from <A HREF="../ST/STShellSetApply.html#STShellSetApply">STShellSetApply</A>().
<P>
The preconditioner matrix K typically depends on the value of the shift, and
its inverse is handled via an internal <A HREF="https://petsc.org/release/manualpages/KSP/KSP.html#KSP">KSP</A> object. Normal usage does not
require explicitly calling <A HREF="../ST/STGetOperator.html#STGetOperator">STGetOperator</A>(), but it can be used to force the
creation of K and M, and then K is passed to the <A HREF="https://petsc.org/release/manualpages/KSP/KSP.html#KSP">KSP</A>. This is useful for
setting options associated with the PCFactor (to set MUMPS options, for instance).
<P>
The returned matrix must NOT be destroyed by the user. Instead, when no
longer needed it must be returned with <A HREF="../ST/STRestoreOperator.html#STRestoreOperator">STRestoreOperator</A>(). In particular,
this is required before modifying the <A HREF="../ST/ST.html#ST">ST</A> matrices or the shift.
<P>
A NULL pointer can be passed in Op in case the matrix is not required but we
want to force its creation. In this case, <A HREF="../ST/STRestoreOperator.html#STRestoreOperator">STRestoreOperator</A>() should not be
called.
<P>
<P>
<H3><FONT COLOR="#883300">See Also</FONT></H3>
<A HREF="../ST/STApply.html#STApply">STApply</A>(), <A HREF="../ST/STApplyTranspose.html#STApplyTranspose">STApplyTranspose</A>(), <A HREF="../ST/STSetBalanceMatrix.html#STSetBalanceMatrix">STSetBalanceMatrix</A>(), <A HREF="../ST/STShellSetApply.html#STShellSetApply">STShellSetApply</A>(),
<BR><A HREF="../ST/STGetKSP.html#STGetKSP">STGetKSP</A>(), <A HREF="../ST/STSetShift.html#STSetShift">STSetShift</A>(), <A HREF="../ST/STRestoreOperator.html#STRestoreOperator">STRestoreOperator</A>(), <A HREF="../ST/STSetMatrices.html#STSetMatrices">STSetMatrices</A>()
<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/stsolve.c.html#STGetOperator">src/sys/classes/st/interface/stsolve.c</A>
<P><H3><FONT COLOR="#883300">Examples</FONT></H3>
<A HREF="../../../src/eps/tutorials/ex43.c.html">src/eps/tutorials/ex43.c</A><BR>
<BR><BR><A HREF="./index.html">Index of all ST routines</A>
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