Forgive me if I am misusing the library, but I can't seem to get out the expected result.

For the NBD, with a number-of-successes of 71, and a probability of success of 0.9712 and a value of 1, I would expect the 'DistributionFunction' method to return approx 0.382....

However with your library, doing the following:

var distribution = new NegativeBinomialDistribution(71, 0.9712);
var X = distribution.DistributionFunction(1);

The result of X is 1.1102230246251565E-16

Wolfram alpha indicates the result should be 0.382...:
http://www.wolframalpha.com/input/?x=6&y=3&i=negative+binomial+distribution+n%3D71+p%3D0.9712

I also get this result from the Math.NET libraries by doing the following code:

var distribution = new MathNet.Numerics.Distributions.NegativeBinomial(71, 0.9712);
var X = distribution.CumulativeDistribution(1);

The result of X is 0.382

(See https://dotnetfiddle.net/BfeMuz for sample of MathNet)

Can you confirm that I am using the library as expected, and this is a bug? Or alternatively explain how to get the correct result.

Best,
Jon