[petsc-users] Modify RHS values at each iteration

TAY wee-beng zonexo at gmail.com
Thu Nov 21 01:40:48 CST 2013

On 21/11/2013 2:09 PM, Jed Brown wrote:
> TAY wee-beng <zonexo at gmail.com> writes:
>> Hi,
>> Due to a special case, I need modify RHS values of the system of eqns at
>> each iteration.
>> Hence, what I can do is to solve the eqn using KSPSolve, limit the
>> maxits in KSPSetTolerances to 1, modify the RHS, and then run KSPSolve
>> again.
>> It will loop until it reaches the convergences I specify.
>> My question is if that's the only way,
> There is almost certainly a better way to formulate your problem.

Hi, in that case, do you want any suggestion? Is it possible to apply 
the preconditioner only once at the start, and not at every intermediate 

Thank you!
>> and will it suffer a large drop in speed?
> That algorithm (without RHS modification) reduces to Richardson
> preconditioned by one step of your chosen preconditioned iterative
> method.  This likely converges much worse than a Krylov method.
> Note that in the form you describe, the preconditioner will be applied
> twice and the operator once.

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