The Dawson integral is defined by \exp(-x^2) \int_0^x dt
\exp(t^2). A table of Dawson's integral can be found in Abramowitz &
Stegun, Table 7.5. The Dawson functions are declared in the header file
`gsl_sf_dawson.h'.
Function: double gsl_sf_dawson(double x)
Function: int gsl_sf_dawson_e(double x, gsl_sf_result * result)
These routines compute the value of Dawson's integral for x.