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log

log



Compute the Natural Logarithm

Portability: ISO/ANSI C conforming, UNIX compatible


SYNOPSIS
DESCRIPTION
RETURN VALUE
DIAGNOSTICS
EXAMPLE
RELATED FUNCTIONS
SEE ALSO


SYNOPSIS

#include <math.h>

double log(double x);


DESCRIPTION

log computes the natural log of its argument x . The x argument must be a positive double-precision, floating-point number. The natural log is the inverse of the exponential function.


RETURN VALUE

log returns the natural log of its argument x , expressed as a double-precision, floating-point number.


DIAGNOSTICS

The run-time library writes an error message to the standard error file ( stderr ) if x is a negative number or 0. In this case, the function returns -HUGE_VAL , the largest negative floating-point number that can be represented.

If an error occurs in log , the _matherr routine is called. You supply your own version of _matherr to suppress the diagnostic message or modify the value returned.


EXAMPLE

This example computes the natural log of 10, using log :

#include <math.h>
#include <stdio.h>

main()
{
   double y, val;
   val = 10.0;
   y = log(val);
   printf("log(%f) = %f\n", val, y);
}


RELATED FUNCTIONS

log10 , _matherr


SEE ALSO


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