PETSC_EXTERN void PETSC_STDCALL matnestgetsubmats_(Mat *A,PetscInt *M,PetscInt *N,Mat *sub,int *ierr)
{
PetscInt i,j,m,n;
Mat **mat;
CHKFORTRANNULLINTEGER(M);
CHKFORTRANNULLINTEGER(N);
CHKFORTRANNULLOBJECT(sub);
*ierr = MatNestGetSubMats(*A,&m,&n,&mat);
if (M) {
*M = m;
}
if (N) {
*N = n;
}
if (sub) {
for (i=0; i<m; i++) {
for (j=0; j<n; j++) {
sub[j + n * i] = mat[i][j];
}
}
}
}
static PetscErrorCode FormJacobian1_block(SNES snes,Vec x,Mat *jac,Mat *B,MatStructure *flag,void *dummy)
{
Vec *xx, x1,x2;
PetscScalar xx_0, xx_1;
PetscInt index,nb;
PetscScalar A_00, A_01, A_10, A_11;
Mat j11, j12, j21, j22;
Mat **mats;
PetscErrorCode ierr;
PetscFunctionBegin;
/* get blocks for solution */
ierr = VecNestGetSubVecs( x, &nb, &xx );
CHKERRQ(ierr);
x1 = xx[0];
x2 = xx[1];
/* get solution values */
index = 0;
ierr = VecGetValues( x1,1, &index, &xx_0 );
CHKERRQ(ierr);
ierr = VecGetValues( x2,1, &index, &xx_1 );
CHKERRQ(ierr);
/* get block matrices */
ierr = MatNestGetSubMats(*jac,PETSC_NULL,PETSC_NULL,&mats);
CHKERRQ(ierr);
j11 = mats[0][0];
j12 = mats[0][1];
j21 = mats[1][0];
j22 = mats[1][1];
/* compute jacobian entries */
A_00 = 2.0*xx_0 + xx_1;
A_01 = xx_0;
A_10 = xx_1;
A_11 = xx_0 + 2.0*xx_1;
/* set jacobian values */
ierr = MatSetValue( j11, 0,0, A_00, INSERT_VALUES);
CHKERRQ(ierr);
ierr = MatSetValue( j12, 0,0, A_01, INSERT_VALUES);
CHKERRQ(ierr);
ierr = MatSetValue( j21, 0,0, A_10, INSERT_VALUES);
CHKERRQ(ierr);
ierr = MatSetValue( j22, 0,0, A_11, INSERT_VALUES);
CHKERRQ(ierr);
*flag = SAME_NONZERO_PATTERN;
/* Assemble sub matrix */
ierr = MatAssemblyBegin(*jac,MAT_FINAL_ASSEMBLY);
CHKERRQ(ierr);
ierr = MatAssemblyEnd(*jac,MAT_FINAL_ASSEMBLY);
CHKERRQ(ierr);
PetscFunctionReturn(0);
}