Hello,

I tried adapting the example NSE.edp in the FreeFem documentation to be fully periodic on the square. I get the error

Problem build of FEspace (2d) (may be : due to periodic Boundary condition missing ) FH

The number of DF must be 3600 and it is 3803

I am hoping someone can point me to an example. The critical part of my code is below.

Thanks,

## Mike

fespace Xh(Th, P2, periodic=[[2, y], [4, y], [1, x], [3, x]]); //velocity component space

fespace Mh(Th, P1, periodic=[[2, y], [4, y], [1, x], [3, x]]); //pressure space

real dt = 0.01, nu=.1;

real alpha=20/dt;

Xh u2, v2, up1, up2;

Xh u1, v1, f1, f2;

Mh p, q;

problem NS (u1, u2, p, v1, v2, q, solver=Crout, init=i)

= int2d(Th)(

alpha*(u1*v1 + u2*v2)

+ nu * (

dx(u1)*dx(v1) + dy(u1) dy(v1)*dy(v2)

+ dx(u2)dx(v2) + dy(u2)dy(v2)

)

- pq(0.000001)

- pdx(v1) - p

- dx(u1)

*q - dy(u2)*v2)

*q*

)

+ int2d(Th)(

- (f1v1+f2)

+ int2d(Th)(

- (f1

)

+ int2d(Th)(

- alpha*convect([up1,up2],-dt,up1)

*v1*

- alphaconvect([up1,up2],-dt,up2)*v2

- alpha

)

;