# Real_polygamma

Real-polygamma-func

## Definition:

evaluates an approximation to the kth derivative of the psi function by

where x is real with x≠0, -1, -2, ... and k=0,1,......6.

For more information please review the s14aec function in the NAG document.

## Parameters:

- x (input, double)
- The argument x of the function.
- Constraint: x must not be 'too close' to a non-positive integer.
- k (input, double)
- The argument k of the function.
- Constraint: 0≤k≤6
- (output, double)
- Approximation to the kth derivative of the psi function .