d.elem(i,j) = l.elem(i,j) + r.elem(i,j);
d.elem(i,j) = +l.elem(i,j);
operator+(const PMatrix<T1,N,C>& l, const PMatrix<T2,N,C>& r){  typename BinaryReturn<PMatrix<T1,N,C>, PMatrix<T2,N,C>, OpAdd>::Type_t  d;  for(int i=0; i < N; ++i)    for(int j=0; j < N; ++j)      d.elem(i,j) = l.elem(i,j) + r.elem(i,j);  return d;}