C in a Nutshell

Name

expm1

Synopsis

Calculates the natural exponential of a number, minus one

#include <math.h>
doubleexpm1( double x );
float expm1f( float x );
long double expm1l( long double x );

The return value of the expm1() function is one less than e raised to the power of the function’s argument, or e^x, where e is Euler’s number, 2.718281.... The expm1() function is designed to yield a more accurate result than the expression exp(x)-1, especially when the value of the argument is close to zero. If the result is beyond the range of the function’s type, a range error occurs.

Example

/* let y = (−e^(−2x) − 1 ) / (e^(−2x) + 1), for certain values of x */

double w, x, y;
if (( x > 1.0E-12 ) && ( x < 1.0 ))
{  w =expm1( -(x+x) );
  y = − w / ( w + 2.0 );
}
else
  /* ... handle other values of x ... */

See Also

exp(), log1p(), log()