d_projection_dx.h

The projection for yield-stress rheology – its derivative.

The projection for yield-stress rheology – its derivative

#include "projection.h"
struct d_projection_dx {
  Float operator() (const Float& x) const {
    if (fabs(x) <= a) return 0;
    if (n == 1) return 1/(c + r);
    if (r == 0) return pow(fabs(x)-a,-1+1/n)/(n*pow(c,1/n));
    return 1/(r + n*c*pow(_phi(fabs(x)-a),-1+n));
  }
  d_projection_dx (Float a1, Float n1=1, Float c1=1, Float r1=0)
   : a(a1), n(n1), c(c1), r(r1), _phi(n1,c1,r1) {}
  Float a,n,c,r;
  phi _phi;
};