scipy.special.pdtri

scipy.special.pdtri(x1, x2[, out])

m=pdtri(k,y) returns the Poisson variable m such that the sum from 0 to k of the Poisson density is equal to the given probability y: calculated by gammaincinv( k+1, y). k must be a nonnegative integer and y between 0 and 1.