Function is_sorted

test/sparse_permutations.cpp:23–35

template<typename T>
bool is_sorted(const T& mat) {
  for(Index k = 0; k<mat.outerSize(); ++k)
  {
    Index prev = -1;
    for(typename T::InnerIterator it(mat,k); it; ++it)
    {
      if(prev>=it.index())
        return false;
      prev = it.index();
    }
  }
  return true;
}

template<typename T>
typename internal::nested_eval<T,1>::type eval(const T &xpr)