1EXPM1(3)                   Linux Programmer's Manual                  EXPM1(3)
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NAME

6       expm1, expm1f, expm1l - exponential minus 1
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SYNOPSIS

9       #include <math.h>
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11       double expm1(double x);
12       float expm1f(float x);
13       long double expm1l(long double x);
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15       Link with -lm.
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17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       expm1():
20           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
21           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
22           _POSIX_C_SOURCE >= 200112L;
23           or cc -std=c99
24       expm1f(), expm1l():
25           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
26           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
27           or cc -std=c99
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DESCRIPTION

30       expm1(x) returns a value equivalent to
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32           exp(x) - 1
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34       It is computed in a way that is accurate even if the value of x is near
35       zero—a  case where exp(x) - 1 would be inaccurate due to subtraction of
36       two numbers that are nearly equal.
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RETURN VALUE

39       On success, these functions return exp(x) - 1.
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41       If x is a NaN, a NaN is returned.
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43       If x is +0 (-0), +0 (-0) is returned.
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45       If x is positive infinity, positive infinity is returned.
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47       If x is negative infinity, -1 is returned.
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49       If the result overflows, a range error occurs, and the functions return
50       -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
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ERRORS

53       See  math_error(7) for information on how to determine whether an error
54       has occurred when calling these functions.
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56       The following errors can occur:
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58       Range error, overflow
59              errno is set to ERANGE (but see BUGS).   An  overflow  floating-
60              point exception (FE_OVERFLOW) is raised.
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CONFORMING TO

63       C99, POSIX.1-2001.
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BUGS

66       For  some large negative x values (where the function result approaches
67       -1), expm1() raises a bogus underflow floating-point exception.
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69       For some large positive x values, expm1() raises a bogus invalid float‐
70       ing-point exception in addition to the expected overflow exception, and
71       returns a NaN instead of positive infinity.
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73       Before version 2.11, the glibc implementation  did  not  set  errno  to
74       ERANGE when a range error occurred.
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SEE ALSO

77       exp(3), log(3), log1p(3)
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COLOPHON

80       This  page  is  part of release 3.53 of the Linux man-pages project.  A
81       description of the project, and information about reporting  bugs,  can
82       be found at http://www.kernel.org/doc/man-pages/.
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86                                  2010-09-12                          EXPM1(3)
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