[BUGFIX] Set element ids before computing volume

Author: chahak13

diffmpm/solver.py

@@ -42,6 +42,7 @@ def __init__(self, mesh, dt, scheme="usf", velocity_update=False):
         self.mesh = mesh
         self.dt = dt
         self.scheme = scheme
+        self.mesh.apply_on_elements("set_particle_element_ids")
         self.mesh.apply_on_particles("compute_volume")
 
     def tree_flatten(self):