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# scipy.special.bdtr

`scipy.special.``bdtr`(k, n, p) = <ufunc 'bdtr'>

  Binomial distribution cumulative distribution function.

  Sum of the terms 0 through k of the Binomial probability density.

  \[\mathrm{bdtr}(k, n, p) = \sum_{j=0}^k {{n}\choose{j}} p^j (1-p)^{n-j}\]

  Parameters: | k : array_like Number of successes (int). n : array_like Number of events (int). p : array_like Probability of success in a single event (float).
  Returns: | y : ndarray Probability of k or fewer successes in n independent events with success probabilities of p.

  Notes

  The terms are not summed directly; instead the regularized incomplete beta function is employed, according to the formula,

  \[\mathrm{bdtr}(k, n, p) = I_{1 - p}(n - k, k + 1).\]

  Wrapper for the Cephes [R371] routine `bdtr`.

  References

  [R371] | (1, 2) Cephes Mathematical Functions Library, http://www.netlib.org/cephes/index.html