AC_ARG_WITH([gsl],
[AS_HELP_STRING([--with-gsl],
[specify whether to build test programs requiring the GNU Scientific Library. [default=auto]]
)], [with_gsl=$withval], [with_gsl=auto])
AC_ARG_WITH([gsl],
[AS_HELP_STRING([--with-gsl],
[specify whether to build test programs requiring the GNU Scientific Library. [default=auto]]
)], [with_gsl=$withval], [with_gsl=auto])