clausen, a FORTRAN90 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 GNU LGPL 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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