Fix definition of rho

dune/tectonic/nicefunction.hh

@@ -35,11 +35,11 @@ class RuinaFunction : public NiceFunction {
       : coefficient(coefficient),
         a(a),
         mu(mu),
-        rho(exp(-mu / a)),
         eta(eta),
         normalStress(normalStress),
         compound_state(b * (state - log(eta * L))),
-        h(h) {}
+        h(h),
+        rho(exp(-(mu + compound_state) / a)) {}
 
   /*
     If mu and sigma_n denote the coefficient of friction and the