add 1e-15 to the computation of norm(vel), avoid nan in some special cases

Author: enigne

pinnicle/physics/friction.py

@@ -56,7 +56,7 @@ def _pde(self, nn_input_var, nn_output_var): #{{{
         taub = slice_column(nn_output_var, tauid)
 
         # compute the basal stress
-        u_norm = (u**2+v**2)**0.5
+        u_norm = (u**2+v**2+self.eps**2)**0.5
         f1 = C**2*(u_norm)**(1.0/self.m) - taub
 
         return [f1] #}}}

pinnicle/physics/physics.py

@@ -79,7 +79,7 @@ def vel_mag(self, nn_input_var, nn_output_var, X):
         vid = self.output_var.index('v')
         u = slice_column(nn_output_var, uid)
         v = slice_column(nn_output_var, vid) 
-        vel = (u**2.0 + v**2.0) ** 0.5
+        vel = (u**2.0 + v**2.0 + 1.0e-15**2) ** 0.5
         return vel
 
     def surf_x(self, nn_input_var, nn_output_var, X):