expm1(3M) Mathematical Library Functions expm1(3M)
NAME
expm1, expm1f, expm1l - compute exponential function
SYNOPSIS
cc [ flag... ] file... -lm [ library... ]
#include <math.h>
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);
DESCRIPTION
These functions compute e**x-1.0.
RETURN VALUES
Upon successful completion, these functions return e**x-1.0.
If x is NaN, a NaN is returned.
If x is +-0, +-0 is returned.
If x is -Inf, -1 is returned.
If x is +Inf, x is returned.
ERRORS
These functions will fail if:
Range Error The result overflows.
If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the overflow floating-point exception is raised.
USAGE
The value of expm1(x) can be more accurate than exp(x)-1.0 for small values of x.
The expm1() and log1p(3M) 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 performing calculations with a small daily interest rate). These functions also simplify writing
accurate inverse hyperbolic functions.
An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should
either examine the return value or check the floating point exception flags to detect exceptions.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO
exp(3M), feclearexcept(3M), fetestexcept(3M), ilogb(3M), log1p(3M), math.h(3HEAD), attributes(5), standards(5)
SunOS 5.10 1 Nov 2003 expm1(3M)
