HP-UX Reference (11i v1 00/12) - 3 Library Functions A-M (vol 6)
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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man3/!!!intro.3c
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log1p(3M) log1p(3M)
NAME
log1p() - natural logarithm function
SYNOPSIS
#include <math.h>
double log1p(double x);
DESCRIPTION
The log1p() function computes logarithmic functions.
The log1p() function is equivalent to log(1 + x), but may be more accurate for very small values of x.
The expm1() and log1p() functions are useful to guarantee that financial calculations of (((1+x)**n)-
1)/x,namely:
expm1(n * log1p(x))/x
are accurate when x is very small (for example, when calculating small daily interest rates). These func-
tions also simplify writing accurate inverse hyperbolic functions.
The ISO/ANSI C committee has approved the
log1p() function for inclusion in the C9X draft standard.
To use this function, compile either with the default
-Ae option or with the -Aa
and -D_HPUX_SOURCE
options. Make sure your program includes <math.h>. Link in the math library by specifying -lm
on the
compiler or linker command line.
RETURN VALUE
log1p() returns the natural logarithm of (1 + x).
If x is +INFINITY, log1p() returns +INFINITY.
If x = -1.0,
log1p() returns −HUGE_VAL.
If x is NaN, log1p() returns NaN.
If x < -1.0, log1p() returns NaN and sets errno to [EDOM].
ERRORS
If log1p() fails, errno is set to the following value.
[EDOM] x is less than -1.0.
SEE ALSO
log(3M), expm1(3M), math(5).
STANDARDS CONFORMANCE
log1p():XPG4.2
HP-UX Release 11i: December 2000 − 1 − Section 3−−497
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