[petsc-users] Error when using DMSTAG_UP for array indexing

[Zhang, Sijie]

Hi,

I got an error when using  DMSTAG_UP for DMStagVec array indexing in a 2D 
DMStag Mesh.

I used the following code for accessing the getting the index for local vector 
data stored at the left and up locations (edge).

PetscInt idFup[4], dFleft[4];
for (ii = 0; ii < 4; ii++)
        DMStagGetLocationSlot(ctx->dmF, LEFT, ii, &idFleft[ii]);
for (ii = 0; ii < 4; ii++)
        DMStagGetLocationSlot(ctx->dmF, RIGHT, ii, &idFright[ii]);

And I used the following sample code for getting the data:

a = UArr[ey][ex][idFright[ii]])

However, after the calculation, I found there are weird fluctuations at the 
boundary of the mesh blocks assigned to each processor as shown in the Figure 
below.(The yellow lines, 5 processors were used in this case.) There seemed to 
be a communication error when using DMSTAG_UP. And I also found the value of 
idFright[ii] was much larger than the index for the locations of left, right, 
or elements. It's on a level of 400+, while the other was only like 1 to 10.

Was there any I did wrong when setting up the 2D DMStag?

Thank you and best regards.

Sijie Zhang

[cid:94a295bd-6851-489d-83d8-44d2a6d80314]