# Convergence question

**URL:** <https://calculix.discourse.group/t/convergence-question/1330>\
**Category:** Uncategorized\
**Created:** [November 9, 2022, 1:58pm UTC](https://calculix.discourse.group/t/convergence-question/1330 "2022-11-09T13:58:49Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![JohnAlo](https://avatars.discourse-cdn.com/v4/letter/j/779978/32.png) [@JohnAlo](https://calculix.discourse.group/u/JohnAlo)\
**Post date:** [November 9, 2022, 1:58pm UTC](https://calculix.discourse.group/t/convergence-question/1330/1 "2022-11-09T13:58:49Z")

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Hello,

I have a model with some contact surfaces. The problem is that 20% of the times I try to solve it, Calculix does not converge and maybe sometimes it will produce multiple result data sets. Is this something expected? Each time I feed the same .inp file in Calculix so probably it is something randomized in the solvers inside Calculix. Has anybody seen this also?

Thank you in advance!

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**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [November 9, 2022, 2:08pm UTC](https://calculix.discourse.group/t/convergence-question/1330/2 "2022-11-09T14:08:02Z")

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Which version of CalculiX and which solver are you using ? Have you tried improving convergence for this model ?

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**Author:** ![JohnAlo](https://avatars.discourse-cdn.com/v4/letter/j/779978/32.png) [@JohnAlo](https://calculix.discourse.group/u/JohnAlo)\
**Post date:** [November 9, 2022, 2:31pm UTC](https://calculix.discourse.group/t/convergence-question/1330/3 "2022-11-09T14:31:57Z")

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I use Calculix 2.20 and I am using the default solver which is PastiX if I am correct.  
By improving convergence you mean to change the covergence criteria?

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**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [November 9, 2022, 2:44pm UTC](https://calculix.discourse.group/t/convergence-question/1330/4 "2022-11-09T14:44:35Z")

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> [@JohnAlo](#):
>
> I use Calculix 2.20 and I am using the default solver which is PastiX if I am correct.

It would be best to try with other solvers, this one is still relatively new.

> [@JohnAlo](#):
>
> By improving convergence you mean to change the covergence criteria?

This rarely helps. What I mean is changing the model in such a way that it converges better. For example, using displacement control instead of load control.

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**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\
**Post date:** [November 9, 2022, 2:49pm UTC](https://calculix.discourse.group/t/convergence-question/1330/5 "2022-11-09T14:49:12Z")

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I have seen this before on windows + Pastix.

> **[Time Period / Time Step. Nonlinear Static.](https://mecway.com/forum/discussion/1090/time-period-time-step-nonlinear-static)**
>
> Hi, I have found something I can not explain and maybe it might be the response to some convergence issues in the past.

By other hand Pastix Mixed precision internal variable seem to give some issues too.  
Try Pardiso.

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**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\
**Post date:** [November 9, 2022, 3:48pm UTC](https://calculix.discourse.group/t/convergence-question/1330/6 "2022-11-09T15:48:27Z")

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Hi, I’m interested in this topic…could you post the .inp file for this problem? many thanks.