2 @cindex Lambert function
4 Lambert's W functions, @math{W(x)}, are defined to be solutions
5 of the equation @math{W(x) \exp(W(x)) = x}. This function has
6 multiple branches for @math{x < 0}; however, it has only
7 two real-valued branches. We define @math{W_0(x)} to be the
8 principal branch, where @math{W > -1} for @math{x < 0}, and
10 @math{W_@{-1@}(x)} to be the other real branch, where
11 @math{W < -1} for @math{x < 0}. The Lambert functions are
12 declared in the header file @file{gsl_sf_lambert.h}.
15 @deftypefun double gsl_sf_lambert_W0 (double @var{x})
16 @deftypefunx int gsl_sf_lambert_W0_e (double @var{x}, gsl_sf_result * @var{result})
17 These compute the principal branch of the Lambert W function, @math{W_0(x)}.
18 @comment exceptions: GSL_EDOM, GSL_EMAXITER
21 @deftypefun double gsl_sf_lambert_Wm1 (double @var{x})
22 @deftypefunx int gsl_sf_lambert_Wm1_e (double @var{x}, gsl_sf_result * @var{result})
23 These compute the secondary real-valued branch of the Lambert W function,
26 @comment exceptions: GSL_EDOM, GSL_EMAXITER