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
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 5.11 12 Jul 2006 expm1(3M)
Check Out this Related Man Page
EXPM1(P) POSIX Programmer's Manual EXPM1(P)
NAME
expm1, expm1f, expm1l - compute exponential functions
SYNOPSIS
#include <math.h>
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);
DESCRIPTION
These functions shall compute e**x-1.0.
An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error
has occurred.
RETURN VALUE
Upon successful completion, these functions return e**x-1.0.
If the correct value would cause overflow, a range error shall occur and expm1(), expm1f(), and expm1l() shall return the value of the
macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.
If x is NaN, a NaN shall be returned.
If x is +-0, +-0 shall be returned.
If x is -Inf, -1 shall be returned.
If x is +Inf, x shall be returned.
If x is subnormal, a range error may occur and x should be returned.
ERRORS
These functions shall fail if:
Range Error
The result overflows.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.
These functions may fail if:
Range Error
The value of x is subnormal.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The value of expm1(x) may be more accurate than exp(x)-1.0 for small values of x.
The expm1() and log1p() 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 calculating small daily interest rates). These functions also simplify writing accurate inverse
hyperbolic functions.
For IEEE Std 754-1985 double, 709.8 < x implies expm1( x) has overflowed.
On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at
least one of them must be non-zero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
exp() , feclearexcept() , fetestexcept() , ilogb() , log1p() , the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment
of Error Conditions for Mathematical Functions, <math.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
online at http://www.opengroup.org/unix/online.html .
IEEE /The Open Group 2003 EXPM1(P)