On Thu, Dec 8, 2016 at 5:10 PM, Khai Pham <[email protected]> wrote:
> Hi Hong, > > I more concern about the difference between A1 and A2 is in the order of > O(1.e-8) as I run the same code twice. Should it be in the order of machine > epsilon? > If you have 17 orders of magnitude difference between elements, then its easy to cancellation when doing subtraction and have differences on that order due to permuted operations. Matt > Khai > > On Thu, Dec 8, 2016 at 4:54 PM, Hong <[email protected]> wrote: > >> Khai : >>> >>> Thanks for your response. The output is not the solution. They are the >>> component of the matrix in matlab format. I would expect the difference in >>> the order of machine precesion. The difference in solutions in two runs is >>> in the order of 1e-5. >>> >> >> If your matrices A1 and A2 have difference of O(1.e-8), then the computed >> solution may differ by >> Condition_number(A) * machine_epsion. Do you know cond(A)? >> >> Please alway send your request to petsc-maint. >> >> Hong >> >>> >>> >>> On Dec 8, 2016 4:01 PM, "Hong" <[email protected]> wrote: >>> >>> Khai : >>> Your solution components have values ranging from 1.e+9 to 1.e-8, and >>> the values only differ in the order of 1.e-8, which are within >>> computational error tolerance. >>> I would consider all solutions same within the approximation tolerance. >>> >>> Hong >>> >>> Hello, >>>> >>>> I have problem with matrix assembly for linear solver KSP. I run the >>>> the same problem with 4 processors multiple time. Using flag >>>> -mat_view ::ascii_matlab to view the matrix. The matrix outputs are not the >>>> same during each run. Please see the attached file for the comparison >>>> between two runs. I checked all the input for each processor as it calls to >>>> MatSetValues ( indices of the matrix and values ) and it's consistent all >>>> the time. I also checked the allocation information (with flag -info) and >>>> it looks fine. Could you give me an advice how to deal with this issue? >>>> Thanks ! >>>> >>>> Best, >>>> Khai >>>> >>> >>> >>> >> > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
