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.TH EXPM1 3M "Jul 12, 2006" "SunOS 5.11" "Mathematical Library Functions"
.SH NAME
expm1, expm1f, expm1l \- compute exponential function
.SH SYNOPSIS
.LP
.nf
c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ]
#include <math.h>

\fBdouble\fR \fBexpm1\fR(\fBdouble\fR \fIx\fR);
.fi

.LP
.nf
\fBfloat\fR \fBexpm1f\fR(\fBfloat\fR \fIx\fR);
.fi

.LP
.nf
\fBlong double\fR \fBexpm1l\fR(\fBlong double\fR \fIx\fR);
.fi

.SH DESCRIPTION
.sp
.LP
These functions compute \fIe\fR^\fIx\fR\(mi1.0.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, these functions return \fIe\fR^\fIx\fR\(mi1.0.
.sp
.LP
If \fIx\fR is NaN, a NaN is returned.
.sp
.LP
If \fIx\fR is \(+-0, \(+-0 is returned.
.sp
.LP
If \fIx\fR is \(miInf, \(mi1 is returned.
.sp
.LP
If \fIx\fR is +Inf, \fIx\fR is returned.
.SH ERRORS
.sp
.LP
These functions will fail if:
.sp
.ne 2
.mk
.na
\fBRange Error\fR
.ad
.RS 15n
.rt
The result overflows.
.sp
If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is
non-zero, the overflow floating-point exception is raised.
.RE

.SH USAGE
.sp
.LP
The value of \fBexpm1(\fR\fIx\fR\fB)\fR can be more accurate than
\fBexp(\fIx\fR)\fR\(mi1.0 for small values of \fIx\fR.
.sp
.LP
The \fBexpm1()\fR and \fBlog1p\fR(3M) functions are useful for financial
calculations of ((1+\fIx\fR)^\fIn\fR\(mi1)/\fIx\fR, namely:
.sp
.in +2
.nf
\fBexpm1(\fIn\fR * log1p(\fIx\fR))\|/\|\fR\fIx\fR
.fi
.in -2

.sp
.LP
when \fIx\fR is very small (for example, when performing calculations with a
small daily interest rate).  These functions also simplify writing accurate
inverse hyperbolic functions.
.sp
.LP
An application wanting to check for exceptions should call
\fBfeclearexcept\fR(\fBFE_ALL_EXCEPT\fR) before calling these functions. On
return, if \fBfetestexcept\fR(\fBFE_INVALID\fR | \fBFE_DIVBYZERO\fR |
\fBFE_OVERFLOW\fR | \fBFE_UNDERFLOW\fR) 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.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
tab(	) box;
cw(2.75i) |cw(2.75i)
lw(2.75i) |lw(2.75i)
.
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR math.h (3HEAD),
.BR exp (3M),
.BR feclearexcept (3M),
.BR fetestexcept (3M),
.BR ilogb (3M),
.BR log1p (3M),
.BR attributes (7),
.BR standards (7)