message: reserve storage in matrix_data constructor
diff: @@ -169,6 +169,7 @@ struct matrix_data {
  if (is_zero(value)) {
  return;
  }
  + nonzeros.reserve(size[0] * size[1]);
  for (size_type row = 0; row < size[0]; ++row) {
  for (size_type col = 0; col < size[1]; ++col) {
  nonzeros.emplace_back(row, col, value);
  @@ -190,6 +191,7 @@ struct matrix_data {
  matrix_data(dim<2> size_, RandomDistribution&& dist, RandomEngine&& engine)
  : size{size_}
  {
  + nonzeros.reserve(size[0] * size[1]);
  for (size_type row = 0; row < size[0]; ++row) {
  for (size_type col = 0; col < size[1]; ++col) {
  const auto value =
  