Use h_pert to modify smoothing lengths.

tests/test27cells.c

@@ -122,7 +122,7 @@ struct cell *make_cell(size_t n, double *offset, double size, double h,
             break;
         }
         if (h_pert)
-          part->h = size * h * random_uniform(1.f, 1.1f) / (float)n;
+          part->h = size * h * random_uniform(1.f, h_pert) / (float)n;
         else
           part->h = size * h / (float)n;
         h_max = fmaxf(h_max, part->h);