STEP-77: fix bug

diff --git a/examples/step-77/step-77.cc b/examples/step-77/step-77.cc
index 3f8a5bc3797129a7cbf9a9c65b25ff5fa19ef89b..ff6cfb319d1dede1d15cece14886010267864813 100644 (file)
--- a/examples/step-77/step-77.cc
+++ b/examples/step-77/step-77.cc
@@ -364,7 +364,7 @@ namespace Step77
                                     evaluation_point_gradients[q]);
 
             for (unsigned int i = 0; i < dofs_per_cell; ++i)
-              cell_residual(i) =
+              cell_residual(i) +=
                 (fe_values.shape_grad(i, q)      // \nabla \phi_i
                  * coeff                         // * a_n
                  * evaluation_point_gradients[q] // * \nabla u_n