let summary = [{
Compute the polygamma function \\(\psi^{(n)}(x)\\).
  }];

  let description = [{
The polygamma function is defined as:


\\(\psi^{(a)}(x) = \frac{d^a}{dx^a} \psi(x)\\)

where \\(\psi(x)\\) is the digamma function.
The polygamma function is defined only for non-negative integer orders \\a\\.
  }];

  let arguments = (ins