[petsc-users] Question about TSComputeRHSJacobianConstant

[Zhang, Hong]

Sajid,

I have also rested the simpler problem you provided. The branch hongzh/fix-computejacobian gives exactly the same numerical results as the master branch does, but runs much faster. So the solver seems to work correctly.

To rule out the possible compiler issues, you might want to try a different compiler or different optimization flags. Also you might want to try smaller stepsizes.

Hong

On May 20, 2019, at 4:47 PM, Sajid Ali <sajidsyed2021 at u.northwestern.edu<mailto:sajidsyed2021 at u.northwestern.edu>> wrote:

Hi Hong,

I tried running a simpler problem that solves the equation ` u_t = A*u_xx + A*u_yy; ` and the fix-computejacobian branch works for this on a coarse grid. The code for the same is here : https://github.com/s-sajid-ali/xwp_petsc/blob/master/2d/FD/free_space/ex_dmda.c and it requires no input file. It writes at all times steps and comparing the output at the last time step, everything looks fine.

I want to eliminate a possible source of error which could be the fact that I installed both versions (3.11.2 and fix-computejacobian) with intel compilers and O3. Could floating point errors occur due to this ? I didn't specify -fp-model strict but since the results I got were reasonable I never bothered to run a test suite.

Thank You,
Sajid Ali
Applied Physics
Northwestern University

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