petsc-master 2020-08-10
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# DMGlobalToLocalSolve

Solve for the global vector that is mapped to a given local vector by DMGlobalToLocalBegin()/DMGlobalToLocalEnd() with mode = INSERT_VALUES. It is assumed that the sum of all the local vector sizes is greater than or equal to the global vector size, so the solution is a least-squares solution. It is also assumed that DMLocalToGlobalBegin()/DMLocalToGlobalEnd() with mode = ADD_VALUES is the adjoint of the global-to-local map, so that the least-squares solution may be found by the normal equations.

### Synopsis

```#include "petscdm.h"
#include "petscdmplex.h"
#include "petscksp.h"
PetscErrorCode DMGlobalToLocalSolve(DM dm, Vec x, Vec y)
```
collective

### Input Parameters

 dm - The DM object x - The local vector y - The global vector: the input value of globalVec is used as an initial guess

### Output Parameters

y -The least-squares solution

Note: If the DM is of type DMPLEX, then y is the solution of L' * D * L * y = L' * D * x, where D is a diagonal mask that is 1 for every point in the union of the closures of the local cells and 0 otherwise. This difference is only relevant if there are anchor points that are not in the closure of any local cell (see DMPlexGetAnchors()/DMPlexSetAnchors()).