Update flow_statistics.py

src/lbmpy/flow_statistics.py

@@ -72,6 +72,7 @@ def welford_assignments(field, mean_field, sum_of_products_field=None):
         for i in range(dim):
             main_assignments.append(
                 ps.Assignment(delta2[i], welford_field.at_index(i) - welford_mean_field.at_index(i)))
+        for i in range(dim):
             for j in range(dim):
                 idx = i * dim + j
                 main_assignments.append(ps.Assignment(