Evaluate lambda function for Affine Wigner distribution.
Y=lambdak(U,K)
real vector
value of LAMBDAD at point(s) U
lambdak evaluates the parametrization lambda function involved in the affine smoothed pseudo Bertrand distribution. lambdak(U,0) = -U/(exp(-U)-1) for K = 0 lambdak(U,1) = exp(1+U exp(-U)/(exp(-U)-1)) for K = 1 lambdak(U,K) = (K (exp(-U)-1)/(exp(-KU)-1))^(1/(K-1)) otherwise