NAME

expm1() − computes exponential functions

SYNOPSIS

#include <math.h>

double expm1(double x);

DESCRIPTION

The expm1() function is equivalent to exp(x) − 1, but may be more accurate for very small values of x.

The expm1() and log1p() functions are useful to guarantee that financial calculations of ­(((1+x)**n)-1)/x, namely:

expm1(n * log1p(x))/x

are accurate when x is very small (for example, when calculating small daily interest rates).  These functions also simplify writing accurate inverse hyperbolic functions. 

To use this function, link in the math library by specifying −lm on the compiler or linker command line. 

RETURN VALUE

If x is +INFINITY, expm1() returns +INFINITY. 

If x is −INFINITY, expm1() returns −1.0. 

If x is NaN, expm1() returns NaN. 

If the correct value after rounding would be smaller in magnitude than MINDOUBLE, expm1() returns zero. 

If the value overflows, expm1() returns HUGE_VAL and sets errno to [ERANGE]. 

ERRORS

If expm1() fails, errno is set to the following value. 

[ERANGE] The result overflows. 

SEE ALSO

exp(3M), log1p(3M), isinf(3M), isnan(3M), values(5). 

STANDARDS CONFORMANCE

expm1(): XPG4.2
 
 

Hewlett-Packard Company  —  HP-UX Release 10.20:  July 1996