[Getdp] specify tangential component of the solution

[wm214 at maths.bath.ac.uk]

I want to enforce an essential boundary condition of the form

         gamma_t u = g

where gamma_t u = u - (n.u)n = (n x u) x n denotes the tangential component
of u, g is a given tangential vector field and n is the outward unit normal.

The getdp manual does not seem to include any example like this one, and none
of the types of constraint listed in section 4.3 looks like it applies here.


Bill McLean.