Initialize solution when printing matrix

Otherwise debugging of nonlinear problems becomes hard.

python/dune/perftool/pdelab/driver/solve.py

@@ -229,6 +229,12 @@ def print_matrix():
     t_v = type_vector(formdata)
 
     return ["if ({}.get<bool>(\"printmatrix\", false)) {{".format(ini),
+            "  // Setup random input",
+            "  std::size_t seed = 0;",
+            "  auto rng = std::mt19937_64(seed);",
+            "  auto dist = std::uniform_real_distribution<>(1., 10.);",
+            "  for (auto& v : {})".format(v),
+            "    v = dist(rng);",
             "  using M = typename {}::Traits::Jacobian;".format(t_go),
             "  M m({});".format(n_go),
             "  {}.jacobian({},m);".format(n_go, v),