3.13

(2004-4-30), revised on 2011-11-03.
2011-11-03 character reference used.

P = ∑e^-λt_kc_k
をλで微分すると、
dP/dλ = -(∑t_ke ^{- λt_k}c_k)
∴dP/dλ = -DP