[petsc-users] accessing individual elements of a global vector created from dmda

Bishesh Khanal bisheshkh at gmail.com
Tue Sep 17 11:06:38 CDT 2013

Dear all,
I have a vector say sol which is a vector created from a dmda with dof = 3.
Now I need to provide an interface to the part of my code which does not
use petsc but needs access to the values of sol.

I was thinking of providing an interface such as:
double solver::getSolutionAtPosition(int x, int y, int z, int field);
which should return a value of the vector sol at the grid position (x,y,z)
and dof = field.

I know how to get the array and loop through all the values such as:
DMDALocalInfo info;
ierr = DMDAGetLocalInfo(da,&info);CHKERRQ(ierr);

Field ***sol;
ierr = DMDAVecGetArray(da,b,&rhs);CHKERRQ(ierr);

    for (PetscInt k = info.zs; k<info.zs+info.zm; ++k) {
        for (PetscInt j = info.ys; j < info.ys+info.ym; ++j) {
            for (PetscInt i = info.xs; i < info.xs+info.xm; ++i) {
                //access sol[k][j][i].vx   or sol[k][j][i].vy or
sol[k][j][i].vz depending on field


But if I have a particular (x,y,z) based on global co-ordinate system, how
do I get the value for the given field ?

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