So I have the code below. It perfectly calculates all the y-points of the polynomial (and prints them to plot with gnuplot), but how do i get the resulting polynomial (1-x² in this case)? 

```
void twoDegreePoly() {
    int n = 3;
    double x[n],y[n];
    printf ("#m=0,S=16\n");
    for (int i=0; i<n ;i++) {
        x[i] = ((double)2*i)/2 -1;
        y[i] = f(x[i]);
        printf ("%g %g\n", x[i], y[i]);
    }
    printf ("#m=1,S=0\n");

    gsl_interp_accel *acc = gsl_interp_accel_alloc ();
    const gsl_interp_type *t = gsl_interp_polynomial;
    gsl_interp* poly = gsl_interp_alloc(t,n);
    gsl_interp_init (poly, x, y,n);
    for (double xi=x[0]; xi<x[n-1]; xi+= 0.01) {
        double yi = gsl_interp_eval (poly, x, y, xi, acc);
        printf ("%g %g\n", xi, yi);
    }
}

```