public static double horner(double x, double y, double[] z){
        double[] b = new double[z.length-1];
        for (int i=(b.length-1); i>=0; i--)b[i]=z[i];
        if(b.length-1<0) return y;
        double c =(y*x)+b[b.length-1];
        return horner(x, c, b);
        }