[petsc-users] nonzero prescribed boundary condition

[Tian(ICT)]

Dear Barry, Thanks a lot for quick answering.
I checked the development documents and found the new version of 
MatZeroRows() does support the nonzero prescribed boundary conditions.

I followed up with more details.
I am using Petasc 2.3.3. to solve a nonlinear problem, e.g. using SNES 
solvers.
I used a displacement-controlled load (as this type of loading works well 
for all cases).
This is the reason the nonzero prescribed boundary came up.

In FormJacobian, I modified Jacobian and residual to satisfy the nonzero 
prescribed boundary.
In FormFunction, I modified the solution to the known solution(this should 
not be necessary as the modified Jacobian and rhs should give the prescribed 
solution also)

Now I found another issue, no matter if I prescried the solution or not in 
FormFunction,
SNES solver always call FormFunction and never call FormJacobian.
Of course the solver finally diverged or converged to a zero solution.

So my quick follow up question is How a displacement-controled load is done 
corrently in Petsc 2.3.3?

Rong

----- Original Message ----- 
From: "Barry Smith" <bsmith at mcs.anl.gov>
To: "PETSc users list" <petsc-users at mcs.anl.gov>
Sent: Tuesday, May 10, 2011 9:31 AM
Subject: Re: [petsc-users] nonzero prescribed boundary condition



   In petsc-dev http://www.mcs.anl.gov/petsc/petsc-as/developers/index.html 
we have modified the calling sequence for MatZeroRows() so that it can 
automatically adjust the appropriate right hand side values for the zeroed 
rows to support zero or non-zero prescribed boundary conditions easily.

    Barry

On May 9, 2011, at 8:18 PM, Tian(ICT) wrote:

> Dear all,
>
> I got this question long ago and searched the prior posting but did not 
> find the solution.
> The question is about nonzero prescribed boundary condition.
> My understanding is that MatZeroRows() works only for zero prescribed 
> value, not non-zero value.
> For the non-zero values, we have to remove the rows associated with the 
> boundary, but this
> will lead to a zero dignal and accordingly the rows in r.h.s should also 
> be removed.
> My question is that does MatZeroRows() also works for nonzero prescribed 
> boundary and if so how to do it simply?
>
> Rong