Turn two divs into a div and two mult

dune/solvers/iterationsteps/obstacletnnmgstep.hh

@@ -274,9 +274,12 @@ class ObstacleTNNMGStep
 
                 for (int j = 0; j < blockSize; ++j)
                 {
+                    auto const inverseCoarseCorrection =
+                        field_type(1) / coarseCorrection_[i][j];
+
                     // compute relative defect constraints
-                    defectConstraint.lower(j) /= coarseCorrection_[i][j];
-                    defectConstraint.upper(j) /= coarseCorrection_[i][j];
+                    defectConstraint.lower(j) *= inverseCoarseCorrection;
+                    defectConstraint.upper(j) *= inverseCoarseCorrection;
 
                     // orient relative defect constraints
                     if (defectConstraint.lower(j) > defectConstraint.upper(j))