A closed-form expression Wk=W0+∑PHq+y:∑P[rom(1,2)nd(3 W+∑;Wq fork=1,2……,r(4 and solving(4) recursⅳey,fork=1,k=2……, we obtain(5)} W rk=1,2,…, where ak=∑p k-1 kA closed-form expression å å - = = = + × + × 1 1 1 0 k i qk i k i Wqk W ri Wqi W r for k r W W W k i i k i i qi qk 1, 2,......, 1 1 1 1 0 = - + × = å å - = = r r å - = = = - - = k i k i k k qk for k r where a a a W W 1 1 0 1, 2,......, (1 )(1 ) r Ë (4) [from (1), (2) and (3)] and solving (4) recursively, for k=1, k=2,….., we obtain (5):