


Clausen Function
================

The Clausen function is defined by the following integral,

.. math::
 \operatorname{Cl_2}(x) = -\int_0^x \log(2 \sin(t/2)) dt

.. index:: Clausen function

It is related to the dilogarithm by

.. math::
  \operatorname{Cl_2}(\theta) =
    \operatorname{Im} \operatorname{Li_2}(\exp(i\theta)).

.. function:: gsl_sf_clausen(x)

 This routine computes the :index:`Clausen integral`
 :math:`\operatorname{Cl_2}(x)`.
