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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.


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.

See also

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


Wrapper for the CDFLIB [R499] Fortran routine cdfnbn.

Formula 26.5.26 of [R500],

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

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

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


[R499](1, 2) Barry Brown, James Lovato, and Kathy Russell, CDFLIB: Library of Fortran Routines for Cumulative Distribution Functions, Inverses, and Other Parameters.
[R500](1, 2) Milton Abramowitz and Irene A. Stegun, eds. Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables. New York: Dover, 1972.