More constness

src/mynonlinearity.cc

@@ -23,7 +23,8 @@ class MyNonlinearity {
   typedef SmallMatrix MatrixType;
 
   // directional subdifferential: at u on the line u + t*v
-  void directionalSubDiff(VectorType u, VectorType v, Interval<double>& D) {
+  void directionalSubDiff(VectorType const u, VectorType const v,
+                          Interval<double>& D) const {
     if (u == SmallVector(0.0)) {
       D[0] = D[1] = func_.rightDifferential(0);
       return;