On Sat, 3 Nov 2012, Ben Gamari wrote:

My digamma package[1] implements an approximation to the digamma
function (due to Tom Minka). Considering that the math-functions package
already has a gamma implementation, it seems it would be natural to
merge digamma into this package.

I've added a digamma implementation: https://github.com/bos/math-functions/commit/6290827ac3054c6e1a49511381dc95a628b82144