poiseuille.h

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struct u : std::unary_function<point,Float> {
  Float operator() (const point& x) const {
    return a*(c+x[1])*(c-x[1]); }
  u (const Float& c1, std::string sc) : c(c1)
   { a = (sc == "cartesian") ? 3/(2*pow(c,3)) : 4/pow(c,4); }
  protected: Float c, a;
};
struct psi : std::unary_function<point,Float> {
  Float operator() (const point& x) const {
    return xy ? a*sqr(c-x[1])*(2*c+x[1]) : a*sqr(c-x[1])*sqr(c+x[1]); }
  psi (const Float& c1, std::string sc) : c(c1), xy(sc == "cartesian")
   { a = xy ? -1/(2*pow(c,3)) : -1/pow(c,4); }
  protected: Float c, a; bool xy;
};