# Compilation error in a code
**URL:** https://community.freefem.org/t/compilation-error-in-a-code/450
**Category:** General Discussion
**Created:** [June 1, 2020, 12:05pm UTC](https://community.freefem.org/t/compilation-error-in-a-code/450 "2020-06-01T12:05:31Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [June 1, 2020, 12:05pm UTC](https://community.freefem.org/t/compilation-error-in-a-code/450/1 "2020-06-01T12:05:31Z")
Dear All,
I am trying to compile a code for non dimensional equation and unfortunately I am getting error (mentioned below):
it seems some value of variable is large that could not be operated within the freefem.
kindly suggest !!!
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### Author:  [@frederichecht](https://community.freefem.org/u/frederichecht)
#### Post date: [June 2, 2020, 2:02pm UTC](https://community.freefem.org/t/compilation-error-in-a-code/450/2 "2020-06-02T14:02:20Z")
Yes,
You use the convect operator with a to high velocity or a velocity with a NaN value, so the method do not works.
remark, in convect operator statically the pass trough n triangle/element where n is more or less
n = velocity/ meshsize and for the method n must be less than 10, and here n \> 1000
best regards,
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### Author:  [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [June 2, 2020, 2:52pm UTC](https://community.freefem.org/t/compilation-error-in-a-code/450/3 "2020-06-02T14:52:23Z")
Dear Sir,
Thanks It helped me a lot.
One, more doubt I have. It would help me further to code system of PDE.
- if we have four governing Eq (PDE) for a model then separately they need to formulate as a problem.
like
problem1(…) = First weak form equation.
problem2(…) = Second weak form equation.
problem3(…) = Third “” “”
problem4(…) = Fourth “”" “”"
after that we can solve it separately.
Am I proceeding in the right direction or only a single equation can deal with the problem.
Kindly suggest something.
Thanks.
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### Author:  [@prj](https://community.freefem.org/u/prj)
#### Post date: [June 2, 2020, 3:03pm UTC](https://community.freefem.org/t/compilation-error-in-a-code/450/4 "2020-06-02T15:03:17Z")
It all depends on the coupling you want to impose between your governing equations. What you describe is usually called weak coupling. If you use a single problem with all governing equations inside, it is usually called strong coupling. What you propose should work fine if your problem is not too stiff.
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### Author:  [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [June 3, 2020, 10:00am UTC](https://community.freefem.org/t/compilation-error-in-a-code/450/5 "2020-06-03T10:00:22Z")
Thanks @prj,
It clarify my doubts regarding defining my problems.
One more point, I am not getting for the stiff nature of problem address by you.
Stiff addresses complexity of the problem or computational cost?
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### Author:  [@prj](https://community.freefem.org/u/prj)
#### Post date: [June 3, 2020, 5:27pm UTC](https://community.freefem.org/t/compilation-error-in-a-code/450/6 "2020-06-03T17:27:25Z")
Very crudely, the stiffness of the system quantifies how each problem is connected with the others.
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### Author:  [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [June 4, 2020, 2:17am UTC](https://community.freefem.org/t/compilation-error-in-a-code/450/7 "2020-06-04T02:17:01Z")
Thanks @prj
now it become easy for me to understand and code a problem in freefem.