Compute the exponential of a number, then subtract 1
#include <math.h> double expm1 ( double x ); float expm1f ( float x );
The expm1() and expm1f() functions compute the exponential of x, minus 1 (e^{x} - 1).
A range error occurs if the magnitude of x is too large.
The value of expm1( x ) may be more accurate than exp( x ) - 1.0 for small values of x.
The expm1() and log1p() functions are useful for financial calculations of (((1+x)**n)-1)/x, namely:
expm1(n * log1p(x))/x
when x is very small (for example, when performing calculations with a small daily interest rate). These functions also simplify writing accurate inverse hyperbolic functions.
The exponential value of x, minus 1.
#include <stdio.h> #include <errno.h> #include <inttypes.h> #include <math.h> #include <fpstatus.h> int main(int argc, char** argv) { double a, b; a = 2; b = expm1(a); printf("(e ^ %f) -1 is %f \n", a, b); return(0); }
produces the output:
(e ^ 2.000000) -1 is 6.389056
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | No |
Signal handler | No |
Thread | Yes |