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

2D cavity flow- without pressure- contour map for temperature, velocity in U and V direction.