[petsc-users] SLEPC no speedup in parallel

[Perceval Desforges]

Dear petsc and slepc developpers, 

I am using slepc to solve an eigenvalue problem. Since I need all the
eigenvalues in a certain interval, I use the spectrum slicing technique
with mumps. However I do not understand: when I run my code with more
than one processor, there is no speedup at all, and it even slows down,
and I don't understand why. 

I wanted to test further and I ran the same code without spectrum
slicing, and asking for about the same amount of eigenvalues. The
calculation was much slower (about 10 times slower), but using more than
one processor sped it up. 

Is this normal behavior or am I doing something wrong? 

Thanks, 

Best regards, 

Perceval,
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