question: @ Reference ( title = "Fast and accurate computation of binomial probabilities" , authors = "C. Loader" , booktitle = "" , url = "http://projects.scipy.org/scipy/raw-attachment/ticket/620/loader2000Fast.pdf" ) private static double devianceTerm ( double x , double np ) { if ( Math . abs ( x - np ) < 0.1 * ( x + np ) ) { final double v = ( x - np ) / ( x + np ) ; double s = ( x - np ) * v ; double ej = 2.0d * x * v ; for ( int j = 1 ; ; j ++ ) { ej *= v * v ; final double s1 = s + ej / ( 2 * j + 1 ) ; if ( s1 == s ) { return s1 ; } s = s1 ; } } return x * Math . log ( x / np ) + np - x ; }
target:  Evaluate the deviance term of the saddle point approximation. bd0(x,np) = x*ln(x/np)+np-x