# Navier Stoke Operation Error
**URL:** https://community.freefem.org/t/navier-stoke-operation-error/478
**Category:** General Discussion
**Created:** [June 19, 2020, 10:18am UTC](https://community.freefem.org/t/navier-stoke-operation-error/478 "2020-06-19T10:18:32Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [June 19, 2020, 10:18am UTC](https://community.freefem.org/t/navier-stoke-operation-error/478/1 "2020-06-19T10:18:32Z")
Dear @prj
I have taken a simple model for Navier Stoke Equation over a square.
which I have taken from [Navier-Stoke](https://doc.freefem.org/tutorials/navierStokesNewton.html).
- I am getting an error as " operation error ".
code is:
```
real nu = 1.0/50.;
real eps = 1e-6;
verbosity = 0;
mesh Th = square(10,10);
fespace Xh(Th, P2);
Xh u1, u2;
Xh du1, du2;
Xh v1, v2;
fespace Mh(Th, P1);
Mh p;
Mh q;
Mh dp;
macro Grad(u1, u2) [dx(u1), dy(u1), dx(u2), dy(u2)] //
macro UgradV(u1, u2, v1, v2) [[u1, u2]' * [dx(v1), dy(v1)], [u1, u2]' * [dx(v2), dy( v2)] ] //
macro div( u1, u2) ( dx(u1) + dy(u2) ) //
// initialization
u1 = x^2 + y^2 ;
u2 = 0;
// viscosity loop
while(1)
{
int n;
real err = 0 ;
for ( n =0; n< 10; n++)
{
solve viscous([du1, du2, dp], [v1, v2, q] ) =
int2d(Th) ( nu *( Grad(u1, u2)' * Grad( v1, v2))
- div( v1, v2)*dp
- div( du1, du2)*q
+ UgradV( du1, du2, u1, u2 )'* [v1, v2]
+ UgradV( u1, u2, du1, du2 )'* [v1, v2]
- 1e-8*dp*q )
- int2d( Th) ( nu * (Grad(u1, u2)'Grad(v1, v2))
+ UgradV( u1, u2, u1, u2)' * [v1, v2]
- p * div(v1, v2 ) - q * div(u1, u2)
)
+ on( 1,2,4, du1 = 0 , du2 = 0 )
+ on ( 3, du1 = 1, du2 = 0 )
u1[] -= du1[];
u2[] -= du2[];
p[] -= dp[];
real Lu1=u1[].linfty, Lu2=u2[].linfty, Lp=p[].linfty;
err = du1[].linfty/Lu1 + du2[].linfty/Lu2 + dp[].linfty/Lp;
cout << n << " err = " << err << " " << eps << " rey = " << 1./nu << endl;
if(err < eps) break; //converge
if( n>3 && err > 10.) break; //blowup
}
}
```
Kindly, suggest me to fix it.
---
### Author:  [@prj](https://community.freefem.org/u/prj)
#### Post date: [June 19, 2020, 10:38am UTC](https://community.freefem.org/t/navier-stoke-operation-error/478/2 "2020-06-19T10:38:01Z")
The example from the documentation works just fine. What did you change?
---
### Author:  [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [June 19, 2020, 10:56am UTC](https://community.freefem.org/t/navier-stoke-operation-error/478/3 "2020-06-19T10:56:36Z")
only, I was trying to run this code over an square domain.
and, rest equations are the same.
But, I am getting the operation error in my case whose code is mentioned above.
I am confused about the operation in my case because the same operation has mentioned in the documentation example [Navier-Stoke](https://doc.freefem.org/tutorials/navierStokesNewton.html).
---
### Author:  [@prj](https://community.freefem.org/u/prj)
#### Post date: [June 19, 2020, 11:28am UTC](https://community.freefem.org/t/navier-stoke-operation-error/478/4 "2020-06-19T11:28:29Z")
You are mixing linear and bilinear terms in your `problem` definition. The code does not look at all like the one from the documentation, if I’m not mistaken.
---
### Author:  [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [June 19, 2020, 5:19pm UTC](https://community.freefem.org/t/navier-stoke-operation-error/478/5 "2020-06-19T17:19:04Z")
I need to rectify it.
Thanks @prj
---
### Author:  [@Duzi100](https://community.freefem.org/u/Duzi100)
#### Post date: [August 21, 2020, 9:47am UTC](https://community.freefem.org/t/navier-stoke-operation-error/478/6 "2020-08-21T09:47:00Z")
Sadly, I have the same error, and I have no idea to fix it.
---
### Author:  [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [August 21, 2020, 12:59pm UTC](https://community.freefem.org/t/navier-stoke-operation-error/478/7 "2020-08-21T12:59:32Z")
It can be solved using linearization technique using Newton’s Method.