log1p

log1p

Logarithm plus 1 function

Portability: C99

SYNOPSIS
DESCRIPTION
RETURN VALUE
DIAGNOSTICS
RELATED FUNCTIONS
SEE ALSO

SYNOPSIS

   #include <math.h>

   double log1p(double x);
   float log1pf(float x);
   long double log1pl(long double x);

DESCRIPTION

log1p computes the natural logarithm of one plus its argument x. This function is expressed by the relation:

y = ln(1 + x)

x must be greater than -1.0.

The function name log1pf should be used for float arguments, and log1pl for long double arguments. Alternately, if the header file tgmath.h is included, log1p may be used with any numeric argument type.

RETURN VALUE

log1p returns the natural logarithm of one plus its argument, provided this value is defined and expressible.

DIAGNOSTICS

If the argument of log1p is invalid, it returns -HUGE_VAL in hexadecimal floating point, or a NaN in binary floating point. In this case, the run-time library writes an error message to the standard error file stderr. log1p(-1.0) returns negative infinity in binary floating point.

RELATED FUNCTIONS

expm1, log, log1p, _matherb, _matherr

SEE ALSO

"Mathematical Functions" in Chapter 2, "Function Categories"

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