do not create mesh tree if not needed

fluid/fluid_problem.c

@@ -35,6 +35,13 @@
 
 #define LOCAL_MATRIX(i,j,a,b) local_matrix[((i)*n_fields*N_SF+N_SF*(a)+(j))*n_fields+(b)]
 
+static MeshTree *get_mesh_tree(FluidProblem *problem)
+{
+  if (problem->mesh_tree == NULL)
+    problem->mesh_tree = mesh_tree_create(problem->mesh);
+  return problem->mesh_tree;
+}
+
 static void particle_force_f(FluidProblem *problem, double *f, double *dfdu, double *dfddp, double *sol, double *dsol, const double *solold, const double c, const double *dc, double a, double dt, int iel, int ip);
 void fluid_problem_interpolate_rho_and_nu(const FluidProblem *problem, double a, double *rho, double *mu) {
   if (problem->n_fluids == 1){
@@ -1626,7 +1633,7 @@ void fluid_problem_set_mesh(FluidProblem *problem, Mesh *mesh) {
   problem->mesh = mesh;
   if(problem->mesh_tree)
     mesh_tree_free(problem->mesh_tree);
-  problem->mesh_tree = mesh_tree_create(mesh);
+  problem->mesh_tree = NULL;
   free(problem->bulk_force);
   problem->bulk_force = malloc(sizeof(double)*mesh->n_nodes*DIMENSION);
   for (int i=0; i<mesh->n_nodes*DIMENSION; ++i)
@@ -1687,7 +1694,7 @@ void fluid_problem_adapt_mesh(FluidProblem *problem, Mesh *new_mesh, int old_n_p
   for (int i = 0;i < new_mesh->n_nodes;++i)
     for (int k = 0; k < D; ++k)
       newx[i*D+k] = new_mesh->x[i*3+k];
-  mesh_tree_particle_to_mesh(problem->mesh_tree,new_mesh->n_nodes, newx, new_eid, new_xi);
+  mesh_tree_particle_to_mesh(get_mesh_tree(problem),new_mesh->n_nodes, newx, new_eid, new_xi);
   for (int i = 0; i < new_mesh->n_nodes; ++i) {
     const int *el = problem->mesh->elements+new_eid[i]*N_N;
     if(new_eid[i] < 0) {
@@ -1734,10 +1741,10 @@ void fluid_problem_adapt_mesh(FluidProblem *problem, Mesh *new_mesh, int old_n_p
     old_particle_element_id[i] = -1;
   }
   double *old_particle_uvw = malloc(sizeof(double)*D*old_n_particles);
-  mesh_tree_particle_to_mesh(problem->mesh_tree, old_n_particles, old_particle_position, old_particle_element_id, old_particle_uvw);
+  mesh_tree_particle_to_mesh(get_mesh_tree(problem), old_n_particles, old_particle_position, old_particle_element_id, old_particle_uvw);
   compute_porosity(problem->mesh, problem->node_volume, problem->oldporosity, old_n_particles, old_particle_position, old_particle_volume, old_particle_element_id, old_particle_uvw, NULL);
 
-  mesh_tree_particle_to_mesh(problem->mesh_tree, problem->n_particles, problem->particle_position, problem->particle_element_id, problem->particle_uvw);
+  mesh_tree_particle_to_mesh(get_mesh_tree(problem), problem->n_particles, problem->particle_position, problem->particle_element_id, problem->particle_uvw);
   compute_porosity(problem->mesh, problem->node_volume, problem->porosity, problem->n_particles, problem->particle_position, problem->particle_volume, problem->particle_element_id, problem->particle_uvw, NULL);
 
   free(old_particle_element_id);
@@ -1750,8 +1757,8 @@ void fluid_problem_set_coordinates(FluidProblem *problem, double *x) {
   }
   if(problem->mesh_tree)
     mesh_tree_free(problem->mesh_tree);
-  problem->mesh_tree = mesh_tree_create(problem->mesh);
-  mesh_tree_particle_to_mesh(problem->mesh_tree, problem->n_particles, problem->particle_position, problem->particle_element_id, problem->particle_uvw);
+  problem->mesh_tree = NULL;
+  mesh_tree_particle_to_mesh(get_mesh_tree(problem), problem->n_particles, problem->particle_position, problem->particle_element_id, problem->particle_uvw);
   compute_porosity(problem->mesh, problem->node_volume, problem->porosity, problem->n_particles, problem->particle_position, problem->particle_volume, problem->particle_element_id, problem->particle_uvw, NULL);
 }
 
@@ -1785,7 +1792,7 @@ void fluid_problem_set_particles(FluidProblem *problem, int n, double *mass, dou
     }
     problem->particle_element_id[i]=-1;
   }
-  mesh_tree_particle_to_mesh(problem->mesh_tree, n, position, problem->particle_element_id, problem->particle_uvw);
+  mesh_tree_particle_to_mesh(get_mesh_tree(problem), n, position, problem->particle_element_id, problem->particle_uvw);
 
   double *c = malloc(sizeof(double)*problem->mesh->n_nodes);
   for (int i = 0; i < problem->mesh->n_nodes; ++i) {
@@ -1817,7 +1824,7 @@ void fluid_problem_move_particles(FluidProblem *problem, int n, double *position
   for (int i = 0; i < n; ++i) {
     old_element_id[i] = problem->particle_element_id[i];
   }
-  mesh_tree_particle_to_mesh(problem->mesh_tree, n, position, problem->particle_element_id, problem->particle_uvw);
+  mesh_tree_particle_to_mesh(get_mesh_tree(problem), n, position, problem->particle_element_id, problem->particle_uvw);
   int *particle_enter = malloc(sizeof(int)*n);
   int *particle_leave = malloc(sizeof(int)*n);
   for (int i = 0; i < n; ++i) {