Introduction - If you have any usage issues, please Google them yourself
duct.f computes a fully developed viscous laminar flow in a rectangular channel of aspect ratio b/a (=bar).
solve the equation:
d^2u/dx^2+ d^2u/dy^2 =-1,-a<x<a,-b<y<b
method of discretisation: 3-point centered differences
method of linear system solution: gauss-seidel+ sor