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mldivide take too much time

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yusuf albadry
yusuf albadry on 14 Mar 2020
Hi guys,
I am solving compressible NS using FEM , and I wrote my solver using MATLAB.
currently I have a problem with the running time ( 90x30 grid ). One time step takes about 22 seconds, 20 seconds of them are in the inverse line ! I dont know why it takes this much time !.

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Walter Roberson
Walter Roberson on 15 Mar 2020
Apparently it can make a big difference.
Walter Roberson
Walter Roberson on 15 Mar 2020
If your matrix is real-valued then if it is symmetric then it is also Hermitian -- equal to its complex transpose.
In such a case if the diagonal is all positive or all negative, then you might be able to use cholesky; if the diagonal does not meet that condition then LDL is used.
yusuf albadry
yusuf albadry on 15 Mar 2020
thank you Walter, for helping, it decreased the time to 50% :)
Thanks for all of you

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Answers (2)

Walter Roberson
Walter Roberson on 18 Mar 2020
To summarize: the most important issue was that the poster had a Ryzen, which is at a disadvantage when using the Intel high performance Math library MKL. Fortunately a user has posted information on how to speed it up; https://www.mathworks.com/matlabcentral/answers/396296-what-if-anything-can-be-done-to-optimize-performance-for-modern-amd-cpu-s#answer_401963 and when the poster did that, they doubled performance.

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Precise Simulation
Precise Simulation on 5 May 2020
You can also try the MUMPS linear solver which is also is up to 30-50% faster than mldivide (Umfpack) in serial mode (and also supports parallel), and is available as pre-compiled Matlab Mex files with the FEATool Multiphysics toolbox

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