I am learning Borel Weil Bott theorem in rational homogeneous varieties. Working on them, I need to know two questions:

1. How to judge if a weight is singular?
2. How to compute the index of a given weight?

For example, let G=B_n, and w=w_1-n*w_2+w_3, where w_i are fundamental weights. How can I determine whether w is singular? If w is not singular, how should I compute the index of w.