Date: 2026-03-01T05:24:36+00:00

Actual source code: daghost.c

      1: /*
      2:   Code for manipulating distributed regular arrays in parallel.
      3: */

      5: #include <petsc/private/dmdaimpl.h>

      7: /*@
      8:   DMDAGetGhostCorners - Returns the global (`i`,`j`,`k`) indices of the lower left
      9:   corner and size of the local region, including ghost points.

     11:   Not Collective

     13:   Input Parameter:
     14: . da - the `DMDA`

     16:   Output Parameters:
     17: + x - the corner index for the first dimension
     18: . y - the corner index for the second dimension (only used in 2D and 3D problems)
     19: . z - the corner index for the third dimension (only used in 3D problems)
     20: . m - the width in the first dimension
     21: . n - the width in the second dimension (only used in 2D and 3D problems)
     22: - p - the width in the third dimension (only used in 3D problems)

     24:   Level: beginner

     26:   Notes:
     27:   Any of `y`, `z`, `n`, and `p` can be passed in as `NULL` if not needed.

     29:   The corner information is independent of the number of degrees of
     30:   freedom per node set with the `DMDACreateXX()` routine. Thus the `x`, `y`, and `z`
     31:   can be thought of as the lower left coordinates of the patch of values on process on a logical grid and `m`, `n`, and `p` as the
     32:   extent of the patch. Where
     33:   grid point has (potentially) several degrees of freedom.

     35: .seealso: [](sec_struct), `DM`, `DMDA`, `DMDAGetCorners()`, `DMDACreate1d()`, `DMDACreate2d()`, `DMDACreate3d()`, `DMDAGetOwnershipRanges()`, `DMStagGetGhostCorners()`, `DMSTAG`
     36: @*/
     37: PetscErrorCode DMDAGetGhostCorners(DM da, PeOp PetscInt *x, PeOp PetscInt *y, PeOp PetscInt *z, PeOp PetscInt *m, PeOp PetscInt *n, PeOp PetscInt *p)
     38: {
     39:   PetscInt w;
     40:   DM_DA   *dd = (DM_DA *)da->data;

     42:   PetscFunctionBegin;
     44:   /* since the xs, xe ... have all been multiplied by the number of degrees
     45:      of freedom per cell, w = dd->w, we divide that out before returning.*/
     46:   w = dd->w;
     47:   if (x) *x = dd->Xs / w + dd->xo;
     48:   if (y) *y = dd->Ys + dd->yo;
     49:   if (z) *z = dd->Zs + dd->zo;
     50:   if (m) *m = (dd->Xe - dd->Xs) / w;
     51:   if (n) *n = (dd->Ye - dd->Ys);
     52:   if (p) *p = (dd->Ze - dd->Zs);
     53:   PetscFunctionReturn(PETSC_SUCCESS);
     54: }