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scipy.special.pdtr

scipy.special.pdtr(x1, x2[, out]) = <ufunc 'pdtr'>

y=pdtr(k,m) returns the sum of the first k terms of the Poisson distribution: sum(exp(-m) * m**j / j!, j=0..k) = gammaincc( k+1, m). Arguments must both be positive and k an integer.