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

EXPM1(3) Linux Programmer's Manual EXPM1(3)
expm1, expm1f, expm1l  exponential minus 1
#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(): _ISOC99_SOURCE  _POSIX_C_SOURCE >= 200112L  _XOPEN_SOURCE >= 500  /* Since glibc 2.19: */ _DEFAULT_SOURCE  /* Glibc versions <= 2.19: */ _BSD_SOURCE  _SVID_SOURCE expm1f(), expm1l(): _ISOC99_SOURCE  _POSIX_C_SOURCE >= 200112L  /* Since glibc 2.19: */ _DEFAULT_SOURCE  /* Glibc versions <= 2.19: */ _BSD_SOURCE  _SVID_SOURCE
These functions return a value equivalent to exp(x)  1 The result 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.
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.
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 errno is set to ERANGE (but see BUGS). An overflow floating point exception (FE_OVERFLOW) is raised.
For an explanation of the terms used in this section, see attributes(7). ┌────────────────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├────────────────────────────┼───────────────┼─────────┤ │expm1(), expm1f(), expm1l() │ Thread safety │ MTSafe │ └────────────────────────────┴───────────────┴─────────┘
C99, POSIX.12001, POSIX.12008.
For some large negative x values (where the function result approaches 1), expm1() raises a bogus underflow floatingpoint exception. For some large positive x values, expm1() raises a bogus invalid floatingpoint exception in addition to the expected overflow exception, and returns a NaN instead of positive infinity. Before version 2.11, the glibc implementation did not set errno to ERANGE when a range error occurred.
exp(3), log(3), log1p(3)
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20160315 EXPM1(3)
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