— Macro: GSL_POSINF

This macro contains the IEEE representation of positive infinity, +\infty. It is computed from the expression +1.0/0.0.

— Macro: GSL_NEGINF

This macro contains the IEEE representation of negative infinity, -\infty. It is computed from the expression -1.0/0.0.

— Macro: GSL_NAN

This macro contains the IEEE representation of the Not-a-Number symbol, NaN. It is computed from the ratio 0.0/0.0.

— Function: int gsl_isnan (const double x)

This function returns 1 if x is not-a-number.

— Function: int gsl_isinf (const double x)

This function returns +1 if x is positive infinity, -1 if x is negative infinity and 0 otherwise.

— Function: int gsl_finite (const double x)

This function returns 1 if x is a real number, and 0 if it is infinite or not-a-number.