# Solving sparse underdetermined linear systems

**URL:** <https://fortran-lang.discourse.group/t/solving-sparse-underdetermined-linear-systems/6472>\
**Category:** Help\
**Created:** [September 5, 2023, 9:08pm UTC](https://fortran-lang.discourse.group/t/solving-sparse-underdetermined-linear-systems/6472 "2023-09-05T21:08:13Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![MarDie](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/mardie/32/54_2.png) [@MarDie](https://fortran-lang.discourse.group/u/MarDie)\
**Post date:** [February 29, 2024, 3:56pm UTC](https://fortran-lang.discourse.group/t/solving-sparse-underdetermined-linear-systems/6472/21 "2024-02-29T15:56:30Z")

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According to [qr\_mumps / qr\_mumps · GitLab](https://gitlab.com/qr_mumps/qr_mumps), StarPU is used for parallelization. I’m pretty sure that there is no MPI parallelization and setting `OMP_NUM_THREADS=1` still gives 0.2 sec.

To me, it seems plausible: Choosing an appropriate algorithm gives normally the larger gain in comparison to parallelization and for sub-second runtimes, overhead and serial sections often prevent any parallel speedup.

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**Author:** ![jacobwilliams](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/jacobwilliams/32/10_2.png) [@jacobwilliams](https://fortran-lang.discourse.group/u/jacobwilliams)\
**Post date:** [March 4, 2024, 3:54am UTC](https://fortran-lang.discourse.group/t/solving-sparse-underdetermined-linear-systems/6472/22 "2024-03-04T03:54:16Z")

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Thanks @MarDie! I was also able to compile it as you say (without parallelization) and it does seem for this size problem, it’s good enough.

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