Petsc slowness on a single processor machine‏

[STEPHANE TCHOUANMO]

Dear all,

I use petsc to solve a nonlinear convection-diffusion type equation in porous media.
The built linear system's size is 30000 and its resolution lasts about a hour on a single processor machine (my laptop...).
I
run for that a hundred time steps and have in average 4 Newton
iterations per time step. So a hour seems huge to me with the optimized
version of Petsc.
I tryed to profile my code with the options
"-log_summary" and "-info". What i get out of it is that the first time
step lasts about 15min representing 25% of the total time and i think
its not normal.
The thing is, these 15min happen at the second call
of the petsc routine "VecScatterCreate()" right after the first Newton residual.

Any idea?
Thanks.

Stephane



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