# Two Different PDE solvers give different answers

**URL:** <https://community.freefem.org/t/two-different-pde-solvers-give-different-answers/674>\
**Category:** General Discussion\
**Created:** [December 3, 2020, 4:04am UTC](https://community.freefem.org/t/two-different-pde-solvers-give-different-answers/674 "2020-12-03T04:04:42Z")\
**Posts on this page:** 1\
**Showing post:** 2

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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:** [December 3, 2020, 6:43am UTC](https://community.freefem.org/t/two-different-pde-solvers-give-different-answers/674/2 "2020-12-03T06:43:10Z")

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As I’ve already told you, put your code between three single quote ```, otherwise it is not copy/paste-able. Make sure it’s runnable, it’s clearly not the case here, e.g., what’s `sigma`?

```auto
code should appear like this;

```

It’s wrong to put the shift in the left-hand side matrix. You have to remove `- sigma u1 * u2` from the varf.

How is this post different than [this](https://community.freefem.org/t/my-computer-keeps-freezing-when-running-freefem/648) one? Also, this question is not related to PDE solvers, but eigensolvers, if I’m not mistaken? What are the eigenvalues you are looking for? Closest to the shift? What are the “analytical results” you are mentioning, i.e., exact values you are supposed to get?

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