if else condition on fenics


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5 months ago by
noname  
Hello everyone,

I am solving a hyperbolic PDE with fenics and using c++. My boundary data is discontinuous and I set the values with

class U : public Expressionclass U : public Expression{public:
U(double eps): _eps(eps) {}
void eval(Array<double>& values, const Array<double>& x)
const {           

if ((x[0]==0.0)and (0.0<x[1]<=0.5)) { values[0]=1.0; }    
  else if ((x[0]==0.0) and (0.5<x[1]<=1.0)) { values[0]=0.0; }
  else if ((x[1]==0.0) and (0.5<x[0]<=1.0)) { values[0]=0.0; }    
  else if ((x[1]==0.0) and (0.0<=x[0]<=0.5)) { values[0]=1.0; }
  else if ((x[0]==1.0) and (0.0<=x[1]<=1.0)) { values[0]=pow(sin(x[1]*M_PI),2); }


but visualizing my solution I see that the boundary data is not correctly set. Anyone knows what I am doing wrong here?

Thanks in advance














Community: FEniCS Project

1 Answer


1
5 months ago by
I'd be worried about comparing two floats exactly (likely to fail due to e.g., truncation). Suggest you try something like abs(x[0]-1)<1e-10 or something like this:
https://fenicsproject.org/pub/tutorial/sphinx1/._ftut1005.html
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