clausen, a C code which evaluates a Chebyshev interpolant to the Clausen function Cl2(x).

Cl2(x) = - integral ( 0 < s < x ) log ( abs ( 2 sin ( x / 2 ) ) ) dx

The Clausen function is periodic, with period 2 pi.


The computer code and data files made available on this web page are distributed under the MIT license


clausen is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

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  1. Kurt Koelbig,
    Chebyshev coefficients for the Clausen function Cl2(x),
    Journal of Computational and Applied Mathematics,
    Volume 64, Number 3, 1995, pages 295-297.

Source Code:

Last revised on 14 June 2019.