[Cleanup] Use Arithmetic

dune/tectonic/mydirectionalconvexfunction.hh

@@ -55,9 +55,9 @@ template <class NonlinearityType> class MyDirectionalConvexFunction {
   double linearPart() const { return b; }
 
   void subDiff(double x, Interval<double> &D) const {
-    VectorType tmp = u;
-    tmp.axpy(x, v);
-    phi.directionalSubDiff(tmp, v, D);
+    VectorType uxv = u;
+    Arithmetic::addProduct(uxv, x, v);
+    phi.directionalSubDiff(uxv, v, D);
     D[0] += A * x - b;
     D[1] += A * x - b;
   }

src/one-body-sample.cc

@@ -447,7 +447,7 @@ int main(int argc, char *argv[]) {
             dampingWriter << "N ";
           } else { // alpha is still the old time step here
             alpha *= damping;
-            alpha.axpy(1.0 - damping, computed_state);
+            Arithmetic::addProduct(alpha, 1.0 - damping, computed_state);
             dampingWriter << "Y ";
           }
           lastCorrection = correction;