[ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |

### 7.11.1 Real Argument

__Function:__double**gsl_sf_dilog***(double*`x`)__Function:__int**gsl_sf_dilog_e***(double*`x`, gsl_sf_result *`result`)These routines compute the dilogarithm for a real argument. In Lewin's notation this is

*Li_2(x)*, the real part of the dilogarithm of a real*x*. It is defined by the integral representation*Li_2(x) = - \Re \int_0^x ds \log(1-s) / s*. Note that*\Im(Li_2(x)) = 0*for*x <= 1*, and*-\pi\log(x)*for*x > 1*.Note that Abramowitz & Stegun refer to the Spence integral

*S(x)=Li_2(1-x)*as the dilogarithm rather than*Li_2(x)*.