Make sure the exact calculation matches the Gadget one when the same kernel function is used.

examples/EAGLE_12/eagle_12.yml

@@ -26,7 +26,7 @@ Statistics:
 # Parameters for the self-gravity scheme
 Gravity:
   eta:                   0.025    # Constant dimensionless multiplier for time integration.
-  epsilon:               0.0000001   # Softening length (in internal units).
+  epsilon:               0.001    # Softening length (in internal units).
   theta:                 0.7      # Opening angle (Multipole acceptance criterion)
   
 # Parameters for the hydrodynamics scheme

src/gravity.c

@@ -436,7 +436,7 @@ void gravity_exact_force_compute_mapper(void *map_data, int nr_gparts,
         a_grav[2] += f * dz;
 
         /* Apply Ewald correction for periodic BC */
-        if (periodic) {
+        if (periodic && r > 1e-5 * hi) {
 
           double corr[3];
 	  gravity_exact_force_ewald_evaluate(dx, dy, dz, corr);