Linux.com

expm1.3

EXPM1

Section: Linux Programmer's Manual (3)
Updated: 2008-08-05
Index Return to Main Contents
 

NAME

expm1, expm1f, expm1l - exponential minus 1  

SYNOPSIS

#include <math.h>

double expm1(double x);

float expm1f(float x);
long double expm1l(long double x);
Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

expm1(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or cc -std=c99
expm1f(), expm1l(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99  

DESCRIPTION

expm1(x) returns a value equivalent to

    exp(x) - 1

It is computed in a way that is accurate even if the value of x is near zero---a case where exp(x) - 1 would be inaccurate due to subtraction of two numbers that are nearly equal.  

RETURN VALUE

On success, these functions return exp(x) - 1.

If x is a NaN, a NaN is returned.

If x is +0 (-0), +0 (-0) is returned.

If x is positive infinity, positive infinity is returned.

If x is negative infinity, -1 is returned.

If the result overflows, a range error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.  

ERRORS

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Range error, overflow
An overflow floating-point exception (FE_OVERFLOW) is raised.

These functions do not set errno.  

CONFORMING TO

C99, POSIX.1-2001.  

BUGS

For some large negative x values (where the function result approaches -1), expm1() raises a bogus underflow floating-point exception.

For some large positive x values, expm1() raises a bogus invalid floating-point exception in addition to the expected overflow exception, and returns a NaN instead of positive infinity.  

SEE ALSO

exp(3), log(3), log1p(3)  

COLOPHON

This page is part of release 3.21 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
BUGS
SEE ALSO
COLOPHON

 

Comments

Subscribe to Comments Feed
Become an Individual Member
Check out the Friday Funnies

Sign Up For the Linux.com Newsletter


Who we are ?

The Linux Foundation is a non-profit consortium dedicated to the growth of Linux.

More About the foundation...

Frequent Questions

Join / Linux Training / Board