Ei(x)
Function:
double
gsl_sf_expint_Ei
(double
x
)
Function:
int
gsl_sf_expint_Ei_e
(double
x
, gsl_sf_result *
result
)
These routines compute the exponential integral E_i(x),
Ei(x) := - PV(\int_{-x}^\infty dt \exp(-t)/t)
where PV denotes the principal value of the integral.