Tribblix: manual page: expm1.3m

EXPM1(3M) Mathematical Library Functions EXPM1(3M)

NAME

expm1, expm1f, expm1l - compute exponential function

SYNOPSIS

c99 [ 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