[Algorit] (minor) Rescale for numerical stability

dune/tectonic/minimisation.hh

@@ -36,7 +36,7 @@ void minimise(Functional const &J, typename Functional::LocalVector &x,
     double const vnorm = v.two_norm();
     if (vnorm <= 0.0)
       return;
-    v *= -1;
+    v /= -vnorm; // normalise for numerical stability; note the minus
 
     double const alpha = lineSearch(J, x, v, bisection);
     Arithmetic::addProduct(x, alpha, v);