# Cos_integral

Cos-integral-func

## Definition:

evaluates

where denotes Euler's constant. The approximation is based on several Chebyshev expansions.

For more information please review the s13acc function in the NAG document.

## Parameters:

- x (input, double)
- The argument x of the function.

- Constraint: x>0.0

- (output, double)
- The approximation of the formula ,x>0