[petsc-users] Slow speed to SetValues for matrix created by PETSC by mat_initial_matrix

[Zhang, Hong]

Check the output of MatMatMult(). If your matrix product has all diagonal entries? How large is your matrix?
Hong

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From: petsc-users <petsc-users-bounces at mcs.anl.gov> on behalf of Yang Juntao <Y.Juntao at hotmail.com>
Sent: Thursday, June 4, 2020 4:01 AM
To: petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: [petsc-users] Slow speed to SetValues for matrix created by PETSC by mat_initial_matrix

Hello,

I computed a preconditioned matrix by MatMatMulti(), and I generated the new matrix with option MAT_INITIAL_MATRIX.

However I need to change the generated matrix by insert value 1 to half of the diagonal. MatSetValue() is used but the speed a much slower than MatSetValue with matrix setup by MatCreate() and MatSeqAIJPreallocation().
I would like to ask is it due to the preallocation setting of MAT_INITIAL_MATRIX generated matrix and how I can change it?

Thanks in advance
JT
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