The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


expm1 - compute exponential functions


#include <math.h>

double expm1 (double x);


The expm1() function computes ex-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.




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

The expm1() and log1p() functions are useful for financial calculations of ((1+x)n-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.




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

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Copyright © 1997 The Open Group
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