13. The computer storage device of claim 11 , further comprising computing forward and backward probabilities and re-estimating the weights.
13. The computer storage device of claim 11 , further comprising computing forward and backward probabilities and re-estimating the weights. 15. The computer-readable medium of claim 13 , wherein re-estimating the weights comprises using: λ k =({tilde over (E)}(f k )−E(f k ))·σ 2 and θ l =({tilde over (E)}(θ l )−E(θ l ))·σ 2 where The σ 2 is a preset parameter to help in avoiding over fitting, vector {tilde over (E)}(f k ) and {tilde over (E)}(θ l ) are actual expectations obtained by counting how often each feature occurs in training data and E(f k ) and E(θ f ) are the estimated expectations.