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); } }
I don't understand the purpose of this code fragment. Are you wanting to copy your K into Kloc? What is the purpose of Kloc? With standard usage of SNES one only needs to provide PETSc a global matrix, one does not need to work with "ghosted" matrices at all. Also normally one fills the f vector in FormFunction and the Jacobian in FormJacobian and there is no need to access the Jacobians at all in SNES https://www.mcs.anl.gov/petsc/documentation/faq.html#functionjacobian <https://www.mcs.anl.gov/petsc/documentation/faq.html#functionjacobian> nor do you need to pass into FormFunction in the context the F or Jacobian matrix. Maybe if you explained your use case a bit more we could make suggestions on how to accomplish it. Barry
On May 19, 2021, at 10:00 AM, Kaushik Vijaykumar <[email protected]> wrote:
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