[petsc-users] Flops pf MatMult is less than expected

Junchao Zhang junchao.zhang at gmail.com
Fri Dec 30 16:30:30 CST 2011

  I have a sparse matrix A. Its size is 494 x 494. It has 1666 nonzeros.
  I call MatMult(A, x, y).  From the profiling result (got by
-log_summary), I find MatMult's flops is 2838.
  I think the flops should be nnz x 2 = 1666 x 2 = 3332.  I don't know how
PETSc got this number (2838).
  I also observed the phenomena with other matrices. It seems PETSc always
give smaller flops.  Why?

 Thank you!
-- Junchao Zhang
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