EXPM1(3) Library Functions Manual EXPM1(3)

expm1 — compute exponential functions

#include <math.h>

double expm1 (double x);

The expm1() function computes e x -1.0.

If x is NaN, then the function returns NaN and errno may be set to EDOM.

If x is positive infinity, expm1() returns positive infinity.

If x is negative infinity, expm1() returns -1.0.

If the value overflows, expm1() returns HUGE_VAL and may set errno to ERANGE.

The expm1() function may fail if:

The value of x is NaN.
The result overflows.

None.

The value of expm1 ( x ) may be more accurate than exp ( x )-1.0 for small values of x .

The expm1() and functions are useful for financial calculations of ((1+ x) -1)/ x, namely:

expm1( n * log1p( x ))/ x
when x is very small (for example, when calculating small daily interest rates). These functions also simplify writing accurate inverse hyperbolic functions.

None.

exp(3) , ilogb(3) , log1p(3) , <math.h> .

February 1997 posix.fail