[petsc-users] Initial estimation on SNES and KSP

[Jed Brown]

Miguel Angel Salazar de Troya <salazardetroya at gmail.com> writes:

> Dear all
>
> SNES uses internally a KSP to solve the linear system of equations right?
> Now the case that we had a linear system of equations that we are solving
> with SNES, how could we set the initial estimation for the KSP? If we just
> included the option -ksp_initial_guess_nonzero, the KSP will grab the
> vector X we passed to the SNES? 

You definitely don't want this for Newton-type methods.  If you have a
nonzero guess for the solution of the linear system, you should have
evaluated the Jacobian at that point.  A zero initial guess is optimal
for Newton-type methods.
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