# Principal Stress/Strain Calculation
**URL:** https://community.freefem.org/t/principal-stress-strain-calculation/398
**Category:** General Discussion
**Created:** [May 10, 2020, 1:51pm UTC](https://community.freefem.org/t/principal-stress-strain-calculation/398 "2020-05-10T13:51:35Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@geoyanzhan3](https://community.freefem.org/u/geoyanzhan3)
#### Post date: [May 10, 2020, 1:51pm UTC](https://community.freefem.org/t/principal-stress-strain-calculation/398/1 "2020-05-10T13:51:35Z")
Hi,
I am building a 2d/3d elasticity model. By following the tutorial (e.g., Beam\_3d.edp), I can solve the stresses {Sxx, Syy, Sxy} (in 2d) or {Sxx, Syy, Szz, Sxy, Syz, Sxz} (in 3d).
Can I further calculate the principal stresses for all elements? Is using EigenValue function a right direction?
Like solving:
`( A - \lambda I )x = 0`
where A is the stress tensor:
A = [Sxx, Sxy, Sxz,
Sxy, Syy, Syz,
Sxz, Syz, Szz]
`\lamba` is 3 eigenvalues
Thank you very much!
Yan
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### Author:  [@prj](https://community.freefem.org/u/prj)
#### Post date: [May 11, 2020, 7:42am UTC](https://community.freefem.org/t/principal-stress-strain-calculation/398/2 "2020-05-11T07:42:40Z")
For small dense matrices, you can use the LAPACK `dgeev` routine, see [here](https://github.com/FreeFem/FreeFem-sources/blob/develop/examples/plugin/lapack.edp#L58) an example. I think that what you want to do is basically loop over your elements and call this routine on all of them?
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### Author:  [@geoyanzhan3](https://community.freefem.org/u/geoyanzhan3)
#### Post date: [May 11, 2020, 12:50pm UTC](https://community.freefem.org/t/principal-stress-strain-calculation/398/3 "2020-05-11T12:50:14Z")
Thank you very much, prj!