[petsc-users] PETSc should not be used to attempt to provide a “parallel linear solver” ??

[Bibrak Qamar]

Hello all,

I am new to PETSc so here comes a newbie question.

On the first page of the manual it says that

"• PETSc should not be used to attempt to provide a “parallel linear
solver” in an otherwise sequential
code. Certainly all parts of a previously sequential code need not be
parallelized but the matrix
generation portion must be parallelized to expect any kind of reasonable
performance. Do not expect
to generate your matrix sequentially and then “use PETSc” to solve the
linear system in parallel.
"
Please help me understand what is meant by it. What if I read the matrix
from a file (sequential) and distribute it to other processes and then call
any linear solver, how is it going to affect the performance of the code?
because reading or generating the matrix is a one time cost for one
timestep, or may be that CAUTION is for multiple timesteps?

Thnaks
Bibrak
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