A viscous flow (with ν = 0.01) in a channel with immobile walls subject to initial conditions u0(x, y) ≡ 1, v0(x, y) ≡ 0. Number of grid points is 128 × 128. The successive solid and dashed lines represent the flow profiles u(y) at times t = 0, .1, .3, .5, … , 1.5.