# Cylindrical Coordinates and the jacobian

**URL:** <https://community.freefem.org/t/cylindrical-coordinates-and-the-jacobian/393>\
**Category:** General Discussion\
**Created:** [May 5, 2020, 10:19pm UTC](https://community.freefem.org/t/cylindrical-coordinates-and-the-jacobian/393 "2020-05-05T22:19:20Z")\
**Posts on this page:** 1\
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**Author:** ![kevinmo08](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/kevinmo08/32/217_2.png) [@kevinmo08](https://community.freefem.org/u/kevinmo08)\
**Post date:** [May 8, 2020, 4:56am UTC](https://community.freefem.org/t/cylindrical-coordinates-and-the-jacobian/393/3 "2020-05-08T04:56:44Z")

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Thank you Julien.

That does help, though I think your last screenshot is over my head a bit.

And I realize sheepishly that it does include the Jacobian now that I went through it again.

I think my confusion stems from the fact that I am trying to run FEM simulations in a sort of weird coordinate system with an equation that I believe is correct. But I am getting strange results that are unphysical when I try to switch from a problem involving cartesian coordinates plus an extra one to one involving polar coordinates plus an extra one, and so I thought maybe the error came from there.  
Which I mention here.

> [@Variational Formulation in Polar Coordinates](https://community.freefem.org/t/variational-formulation-in-polar-coordinates/395/2):
>
> I’m realizing now that the solution in the example does have the jacobian in it, but for some reason my correct equation below is still not working. Are there other issues with polar coordinates I am not aware of? 0 = int2d(Th)(x^2\*(a\*dx(u)\*dx(v) + dy(u)\*dy(v) )) // bilinear form + int2d(Th)( (x^2\*cos(y)\*dx(u)\*v + x\*cos(y)\*v\*u) // linear form + any boundary conditions.

Anyway. Thanks Again!

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