Now PETSc treats the multigrid based on the half spacing strategy, thus they always do odd number of grids.
R Quoting Ryan Yan <vyan2000 at gmail.com>: > Sorry, I forgot to cc to the group. > > BTW, if this is designed to have only odd number of points on the finer > level grid, can anyone provide a hint on the reasoning behind this? > > Thanks a lot, > > Yan > > On Tue, Dec 15, 2009 at 10:09 PM, Ryan Yan <vyan2000 at gmail.com> wrote: > >> Hi Rebecca, >> Thanks for the info. I noticed that rule; yet, it seems very difficult to >> bring up a finest grid with *even* number of pts. >> >> Yan >> >> >> On Tue, Dec 15, 2009 at 9:55 PM, (Rebecca) Xuefei YUAN < >> xy2102 at columbia.edu> wrote: >> >>> The relation between the coarser grid and finer grid is always half >>> spacing in either x-, y-, or z-direction. >>> >>> Thus, for your finest grid being 257x257x257, you need a coarser grid of >>> 129x129x129 on the coarse grid if your level is 2. >>> >>> Hope this is helpful. >>> >>> R >>> >>> >>> >>> Quoting Ryan Yan <vyan2000 at gmail.com>: >>> >>> Hi All, >>>> I was ignoring the importance of fixing the mesh size. >>>> For instance, if I want to compare the effect of mesh sequencing on the >>>> solver, I will use one level with 256 pt on each direction in 2d, in the >>>> first run. >>>> >>>> My question is, in the second run, how to set up the number of points on >>>> the coarsest grid and pre-fix the level of the grid so that DMMG >>>> can bring me the exact resolution of 256 pt on each direction on the >>>> finest >>>> grid. Only this way, the two different solver are solving the problem of >>>> the >>>> same >>>> size. >>>> >>>> Thanks a lot, >>>> >>>> Yan >>>> >>>> >>> >>> >>> -- >>> (Rebecca) Xuefei YUAN >>> Department of Applied Physics and Applied Mathematics >>> Columbia University >>> Tel:917-399-8032 >>> www.columbia.edu/~xy2102 <http://www.columbia.edu/%7Exy2102> >>> >>> >> > -- (Rebecca) Xuefei YUAN Department of Applied Physics and Applied Mathematics Columbia University Tel:917-399-8032 www.columbia.edu/~xy2102
