[petsc-users] Using SNES to solve Non linear elasticity, passing matrix to form function

[Kaushik Vijaykumar]

Hi everyone,

We are in the process of integrating nonlinear solution to our FE code
through SNES. The first steps that I understood that need to be done is to
be able to pass the assembled stiffness matrix K and force vector F to the "
*formfunction*" to calculate the residual and "*formjacobian*" to calculate
the tangent stiffness matrix. To do so, I have defined a struct:


*extern PetscErrorCode FormJacobian(SNES,Vec,Mat,Mat,void*);extern
PetscErrorCode FormFunction(SNES,Vec,Vec,void*);*

// define a struct type to pass K and f as "user context"




*typedef struct    {      Mat K;      Vec f;    } K_and_f;*

In the main program, the struct is declared
*int main()*
*{*
*K_and_f main_K_and_f;* // declare the struct

// SNES - Populate K and f into the struct
*main_K_and_f.K = K;* // K matrix
*main_K_and_f.f = f; *// f vector
....
....
*}*
In form function








*PetscErrorCode FormFunction(SNES snes, Vec x, Vec F, void* ctx) {
PetscErrorCode ierr;    PetscReal *ax,*c;    PetscReal *aF;    PetscScalar
*Kc,v;     PetscInt nlocal,m,n,i,j,index[100000];   * // Create local Vec
and Mat
*    Mat Kloc;*
*    Vec Floc, Uloc, KUloc, resloc;*

*    K_and_f* ptr = (K_and_f*) ctx; *// cast the pointer to void into
pointer to struct
    // Get local F array, FLOC
*    ierr = VecGhostGetLocalForm(ptr->f,&Floc);CHKERRQ(ierr);*


I am able to get the f array from the main program using "
VecGhostGetLocalForm" and the vec is correct. However, I am having trouble
with reading the K matrix in formfunction.

The following trial gives me incorrect K values in Kloc:
*ierr = MatSeqAIJGetArray(ptr->K,&Kc);CHKERRQ(ierr); *

*ierr = MatGetLocalSize(ptr->K,&m,&n); CHKERRQ(ierr);*







*for(i=0;i<m;i++)    {       for(j=0;j<n;j++)      {        v  = *(Kc +
(i*n+j));        ierr =
MatSetValues(Kloc,1,&i,1,&j,&v,INSERT_VALUES);CHKERRQ(ierr);      }*
*    } *

    When I compare K and Kloc, they are not identical


Please let me know if there is an equivalent function like
*VecGhostGetLocalForm()* for Matrices. If not, is there a better way to do
this.

Any guidance/help is greatly appreciated.

Thanks
Kaushik
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20210519/1fc2a7ea/attachment.html>