fix a segmentation fault bug of mc due to mergence

Author: Weiwei Wang

examples/mc/skx.py

@@ -14,7 +14,7 @@ def run(mesh):
     mc = MonteCarlo(mesh, name='test1')
     mc.set_m(random_m)
     J = 50*const.k_B
-    mc.set_options(H=[0,0,0.0], J=J, D=0.27*J, T=4.0)
+    mc.set_options(H=[0,0,1.0], J=J, D=0.27*J, T=4.0)
     mc.run(steps=100000, save_m_steps=None, save_vtk_steps=50000, save_data_steps=50000)
 
 if __name__=='__main__':

fidimag/atomistic/lib/mc.c

@@ -165,8 +165,8 @@ void run_step_mc(mt19937_state *state, double *spin, double *new_spin,
       delta_E += compute_deltaE_exchange_DMI_hexagonal(
           &spin[0], &new_spin[0], &ngbs[0], n_ngbs, J, D, i, new_i);
     } else {
-      delta_E += compute_deltaE_exchange_DMI(&spin[0], &new_spin[0], &ngbs[0], n_ngbs,
-                                             &nngbs[0], J, J1, D, D1, i, new_i);
+      delta_E += compute_deltaE_exchange_DMI(&spin[0], &new_spin[0], &ngbs[0], 
+                                             &nngbs[0], n_ngbs, J, J1, D, D1, i, new_i);
     }
 
     update = 0;