fixed Prestress in ViscoResidual

src/elasticity/assemble/IElasticity.hpp

@@ -77,8 +77,9 @@ public:
   double Residual(const Vector &u, Vector &r) const override {
     r = *Prestress;
     r = 0;
-    for (cell ce = u.cells(); ce != u.cells_end(); ++ce)
+    for (cell ce = u.cells(); ce != u.cells_end(); ++ce) {
       Residual(ce, u, r);
+    }
     r.ClearDirichletValues();
     r.Collect();
     return r.norm();
@@ -101,8 +102,9 @@ public:
   /// Calculates the residual including viscous part.
   virtual double ViscoResidual(const Vector &u, const Vector &v, Vector &defect) const {
     defect = *Prestress;
+    defect = 0;
     TRY {
-      for (cell ce = v.cells(); ce != v.cells_end(); ++ce)
+      for (cell ce = u.cells(); ce != u.cells_end(); ++ce)
         ViscoResidual(ce, u, v, defect);
     } CATCH ("Error in Residual")
     defect.ClearDirichletValues();