GNU Scientific Library Reference Manual - Third Edition (v1.12) by M. Galassi, J. Davies, J. Theiler, B. Gough, G. Jungman, P. Alken, M. Booth, F. Rossi Paperback (6"x9"), 592 pages, 60 figures ISBN 0954612078 RRP £24.95 ($39.95) Get a printed copy>>>

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4.2 Infinities and Not-a-number

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.⁽⁴⁾

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.