# scipy.special.nbdtrin¶

scipy.special.nbdtrin(k, y, p) = <ufunc 'nbdtrin'>

Inverse of nbdtr vs n.

Returns the inverse with respect to the parameter n of y = nbdtr(k, n, p), the negative binomial cumulative distribution function.

Parameters: k : array_like The maximum number of allowed failures (nonnegative int). y : array_like The probability of k or fewer failures before n successes (float). p : array_like Probability of success in a single event (float). n : ndarray The number of successes n such that nbdtr(k, n, p) = y.

nbdtr
Cumulative distribution function of the negative binomial.
nbdtri
Inverse with respect to p of nbdtr(k, n, p).
nbdtrik
Inverse with respect to k of nbdtr(k, n, p).

Notes

Wrapper for the CDFLIB [1] Fortran routine cdfnbn.

Formula 26.5.26 of [2],

$\sum_{j=k + 1}^\infty {{n + j - 1}\choose{j}} p^n (1 - p)^j = I_{1 - p}(k + 1, n),$

is used to reduce calculation of the cumulative distribution function to that of a regularized incomplete beta $$I$$.

Computation of n involves a search for a value that produces the desired value of y. The search relies on the monotonicity of y with n.

References

 [1] (1, 2) Barry Brown, James Lovato, and Kathy Russell, CDFLIB: Library of Fortran Routines for Cumulative Distribution Functions, Inverses, and Other Parameters.
 [2] (1, 2) Milton Abramowitz and Irene A. Stegun, eds. Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables. New York: Dover, 1972.

#### Previous topic

scipy.special.nbdtrik

#### Next topic

scipy.special.ncfdtr