// Andrew Taylor - andrewt@unsw.edu.au
// 6/3/2017

// Demonstrate approximate representation of reals
// producing error.
// sometimes if we subtract two approximations which are very close together
// we can canb get a large relative error
//
// correct answer if x == 0.000000011 (1 - cos(x))  / (x * x) is very close to 0.5
// code prints 0.917540 which is wrong by a factor of almost two

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

int main(void) {
    double x, y;
    x = 0.000000011;
    y = (1 - cos(x))  / (x * x);
    printf("correct answer = ~0.5 but y = %lf\n", y);
    return 0;
}