Firstly, I would like to congratulate the PETSc team for such a great code! I send you an image of my case (all indices are global). Ghost cells are in yellow and white cells are the interior cells. To calculate the gradient at a cell, I use the gauss theorem so I need all neighbor cells for that. The interior points are easy I can calculate them each time in each processor since I have a ghost cell layer. My problem is the gradient in ghost cells because I need the values at pink cells but they belong to another process. I guess I could include these pink cells also as ghost cells and then I would have access to their values. Or I could calculate the gradient and exchange it through processes using VecCreateGhost(). For now I have the code working because I only use these cell-centered gradients for non-orthogonal corrections. So, if the grid orthogonal this term is zero. Quoting Barry Smith <bsmith@mcs.anl.gov>: > > > On Sat, 4 Mar 2006, billy@dem.uminho.pt wrote: > > > > > Hi, > > > > I need the gradient of 5 scalars at ghost cells and I was thinking of > creating > > 5x3 vectors with VecCreateGhost(). Right now, I calculate the gradient > during > > each iteration and I don't store it's value. > > I would like to calculate, store and exchange the gradient at the ghost > cells > > only, to minimize memory requirements. How is the best way to do that? > ^^^^^^^ > Do you not need the gradient values for the interior points? Or are you > > willing to recompute the gradients for the interior points? Why different? > > If the gradient is the same each time why not just calculate it the > first > time and store it for later? Don't make live complicated by using > VecCreateGhost(), just compute them and store them in some array. > > Barry > > > > > > Billy. > > > > > >
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