# Function G2lib::FresnelCS(int_type, real_type, real_type *, real_type *)

- Defined in File Fresnel.cc

## Function Documentation

void G2lib::FresnelCS(int_type nk, real_type x, real_type *C, real_type *S)

  Compute Fresnel integrals and its derivatives

  \[ C(x) = \int_0^x \cos\left(\frac{\pi}{2}t^2\right) dt, \qquad S(x) = \int_0^x \sin\left(\frac{\pi}{2}t^2\right) dt \]
  Parameters

    - nk – maximum order of the derivative

    - x – the input abscissa

    - S – S[0]= \( S(x) \), S[1]= \( S'(x) \), S[2]= \( S''(x) \)

    - C – C[0]= \( C(x) \), C[1]= \( C'(x) \), C[2]= \( C''(x) \)