# Why '-pc\_type hypre' does not converge?

**URL:** <https://community.freefem.org/t/why-pc-type-hypre-does-not-converge/3898>\
**Category:** General Discussion\
**Created:** [May 5, 2025, 11:50am UTC](https://community.freefem.org/t/why-pc-type-hypre-does-not-converge/3898 "2025-05-05T11:50:31Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![zxss](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zxss](https://community.freefem.org/u/zxss)\
**Post date:** [May 5, 2025, 11:50am UTC](https://community.freefem.org/t/why-pc-type-hypre-does-not-converge/3898/1 "2025-05-05T11:50:31Z")

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Dear all,

When I parallelize my code of a 2D lid driven cavity problem. I found that when I choose set(NS, sparams = “-pc\_type lu”) the result is good. But when I choose to use set(NS, sparams = “-pc\_type hypre”, the result is wrong, it shows it doesn’t converge every step.

Does anyone know the reason? Many thanks in advance.  
[2D\_lid\_dirven\_cavity\_parallel.edp](https://community.freefem.org/uploads/short-url/f3t9i3w4HUqX7IOBYY9FFD3jQVK.edp) (2.7 KB)

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**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\
**Post date:** [May 5, 2025, 12:39pm UTC](https://community.freefem.org/t/why-pc-type-hypre-does-not-converge/3898/2 "2025-05-05T12:39:51Z")

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Multiple reasons:

1. you are using the default `tgv` value which is terrible for iterative solvers
2. you are solving a saddle-point problem, and this doesn’t work out-of-the-box for such problems

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<div class="post-metadata">

**Author:** ![zxss](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zxss](https://community.freefem.org/u/zxss)\
**Post date:** [May 5, 2025, 1:34pm UTC](https://community.freefem.org/t/why-pc-type-hypre-does-not-converge/3898/3 "2025-05-05T13:34:20Z")

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I see, many thanks , professor.