## Infinities and Not-a-number

Macro: GSL_POSINF
This macro contains the IEEE representation of positive infinity, @math{+\infty}. It is computed from the expression +1.0/0.0.

Macro: GSL_NEGINF
This macro contains the IEEE representation of negative infinity, @math{-\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 @math{+1} if x is positive infinity, @math{-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.