Calculates the natural exponential of a number, minus one

#include <math.h>
double expm1 ( 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( )