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<div id="version" align=right><b>slepc-3.23.1 2025-05-01</b></div>
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<H1>DSTruncate</H1>
Truncates the system represented in the <A HREF="../DS/DS.html#DS">DS</A> object.
<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/DSTruncate.html#DSTruncate">DSTruncate</A>(<A HREF="../DS/DS.html#DS">DS</A> ds,<A HREF="https://petsc.org/release/manualpages/Sys/PetscInt.html#PetscInt">PetscInt</A> n,<A HREF="https://petsc.org/release/manualpages/Sys/PetscBool.html#PetscBool">PetscBool</A> trim)
</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>n </B></TD><TD> - the new size
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>trim </B></TD><TD> - a flag to indicate if the factorization must be trimmed
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Note</FONT></H3>
The new size is set to n. Note that in some cases the new size could
be n+1 or n-1 to avoid breaking a 2x2 diagonal block (e.g. in real
Schur form). In cases where the extra row is meaningful, the first
n elements are kept as the extra row for the new system.
<P>
If the flag trim is turned on, it resets the locked and intermediate
dimensions to zero, see <A HREF="../DS/DSSetDimensions.html#DSSetDimensions">DSSetDimensions</A>(), and sets the state to RAW.
It also cleans the extra row if being used.
<P>
The typical usage of trim=true is to truncate the Schur decomposition
at the end of a Krylov iteration. In this case, the state must be
changed to RAW so that <A HREF="../DS/DSVectors.html#DSVectors">DSVectors</A>() computes eigenvectors from scratch.
<P>
<P>
<H3><FONT COLOR="#883300">See Also</FONT></H3>
<A HREF="../DS/DSSetDimensions.html#DSSetDimensions">DSSetDimensions</A>(), <A HREF="../DS/DSSetExtraRow.html#DSSetExtraRow">DSSetExtraRow</A>(), <A HREF="../DS/DSStateType.html#DSStateType">DSStateType</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/ds/interface/dsops.c.html#DSTruncate">src/sys/classes/ds/interface/dsops.c</A>
<BR><BR><A HREF="./index.html">Index of all DS routines</A>
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