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<TITLE>Re: Extend preallocation</TITLE>
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----- Original Message -----<BR>
From: owner-petsc-users@mcs.anl.gov <owner-petsc-users@mcs.anl.gov><BR>
To: petsc-users@mcs.anl.gov <petsc-users@mcs.anl.gov><BR>
Sent: Tue Sep 23 21:38:31 2008<BR>
Subject: Extend preallocation<BR>
<BR>
Dear Petsc users,<BR>
<BR>
I would like to compute the sparse projection matrix Q=Id - Pt*A*P.<BR>
<BR>
Pt*A*P is very well computed by MatMatMult ; then I would like to use<BR>
MatShift in order to complete the computation.<BR>
Unfortunately, Pt*A*P has lots of zeros on its diagonal, thus MatShift is<BR>
very slow due to inapropriate preallocation.<BR>
<BR>
Since the initial preallocation of Pt*A*P is very good, I would to know if<BR>
there is a method allowing to get the allocation data structure and to<BR>
extend it in order to preallocate the diagonal terms.<BR>
<BR>
Best regards,<BR>
<BR>
Nicolas<BR>
<BR>
<BR>
<BR>
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