PetscErrorCode ComputeRHS(KSP ksp,Vec b,void *ctx)
{
UserContext *user = (UserContext*)ctx;
PetscErrorCode ierr;
PetscInt i,j,M,N,xm,ym,xs,ys;
PetscScalar Hx,Hy,pi,uu,tt;
PetscScalar **array;
DM da;
MatNullSpace nullspace;
PetscFunctionBeginUser;
ierr = KSPGetDM(ksp,&da);CHKERRQ(ierr);
ierr = DMDAGetInfo(da, 0, &M, &N, 0,0,0,0,0,0,0,0,0,0);CHKERRQ(ierr);
uu = user->uu; tt = user->tt;
pi = 4*PetscAtanReal(1.0);
Hx = 1.0/(PetscReal)(M);
Hy = 1.0/(PetscReal)(N);
ierr = DMDAGetCorners(da,&xs,&ys,0,&xm,&ym,0);CHKERRQ(ierr); /* Fine grid */
ierr = DMDAVecGetArray(da, b, &array);CHKERRQ(ierr);
for (j=ys; j<ys+ym; j++) {
for (i=xs; i<xs+xm; i++) {
array[j][i] = -PetscCosScalar(uu*pi*((PetscReal)i+0.5)*Hx)*PetscCosScalar(tt*pi*((PetscReal)j+0.5)*Hy)*Hx*Hy;
}
}
ierr = DMDAVecRestoreArray(da, b, &array);CHKERRQ(ierr);
ierr = VecAssemblyBegin(b);CHKERRQ(ierr);
ierr = VecAssemblyEnd(b);CHKERRQ(ierr);
/* force right hand side to be consistent for singular matrix */
/* note this is really a hack, normally the model would provide you with a consistent right handside */
ierr = MatNullSpaceCreate(PETSC_COMM_WORLD,PETSC_TRUE,0,0,&nullspace);CHKERRQ(ierr);
ierr = MatNullSpaceRemove(nullspace,b);CHKERRQ(ierr);
ierr = MatNullSpaceDestroy(&nullspace);CHKERRQ(ierr);
PetscFunctionReturn(0);
}
static void func4(PetscReal x, PetscReal *val)
{
const PetscReal u = PetscSqrtReal(2.0 + x*x);
*val = PetscAtanReal(u)/((1.0 + x*x)*u);
}
static void func2(PetscReal x, PetscReal *val)
{
*val = x*x*PetscAtanReal(x);
}
