Hi, I'm facing a real-life problem and I don't what specific mathematics topic it's related to. 1. The problem statement, all variables and given/known data I know the value of the components of a vector field in three points of space and I have to find the flux of this vector field through the surface defined by those points. Lets say that the vector field is the following Q = u(x,y,z)i + v(x,y,z)j The vertical component of the vector field is omitted because I know that the surface is vertical. I know the value of the vector's components (u1,v1), (u2,v2) and (u3,v3) in the coordinates (x1,y1,z1), (x2,y2,z2) and (x3,y3,z3), which may be seen as the vertices of a triangular surface. Linear variations may be assumed for the vector component functions. 2. Relevant equations That's what I'm looking for. 3. The attempt at a solution I've searched a lot for finite element representation of surface fluxes, but I've found nothing what clearly looked similar to my problem.