[petsc-users] real and complex numbers

[Jed Brown]

On Sun, Mar 18, 2012 at 14:52, Barry Smith <bsmith at mcs.anl.gov> wrote:

>  Just run your single code in complex numbers (where the nonlinear part
> may have zero imaginary part). You are introducing a complicated work flow
> (saving to files ...) (that is also not well supported in PETSc) just to
> save some work on the nonlinear part when generally most nonlinear solvers
> spend much more time in the linear solve than the nonlinear computations.
> Make your life easy, just use complex numbers; your time is much more
> valuable than the computers.


Also, if the nonlinear function is very expensive, you can read the state
from the Vec into PetscReal locally (e.g. one stencil at a time) and
compute with reals.

Writing to files creates a _serious_ bottleneck that will likely take
orders of magnitude longer than everything else your code does if you scale
it to large problems/computers.
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