# FEM Weak Form Help

**URL:** <https://community.freefem.org/t/fem-weak-form-help/541>\
**Category:** General Discussion\
**Created:** [August 19, 2020, 8:17am UTC](https://community.freefem.org/t/fem-weak-form-help/541 "2020-08-19T08:17:04Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![sumantkr](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/sumantkr/32/2681_2.png) [@sumantkr](https://community.freefem.org/u/sumantkr)\
**Post date:** [August 19, 2020, 8:17am UTC](https://community.freefem.org/t/fem-weak-form-help/541/1 "2020-08-19T08:17:04Z")

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Can anyone help me to get a weak form coding for equation:

u\_x \* T\_y - u\_y \* T\_x = 0 ---------------------(1)

The weak form as for test fn w is:

- w\_x \* u \* T\_y + w\_y \* u \* T\_x = 0 ---------------------------(2)

And I have written the code for equation (2) as:

`- dx(w) * u * dy(T) + dy(w) * u * dx(T)`

But it shows some error for linearity.

KINDLY SUGGEST ME TO FIX IT.