double rofunc(double b)
{
    int n1,j;
	double nml,nmh;
	double d;
	n1 = ndatat + 1;
    nml = (double)n1 / 2;
    nmh = n1 - nml;
    for (j = 1; j<=ndatat; j++)
	{
        arr[j] = yt[j] - b * xt[j];
    }
    sort(ndatat, arr);
    aa = 0.5 * (arr[(int)nml] + arr[(int)nmh]);
    double sum = 0.0;
    abdevt = 0.0;
    for (j = 1; j<=ndatat; j++)
	{
        d = yt[j] - (b * xt[j] + aa);
        abdevt = abdevt + fabs(d);
        sum = sum + xt[j] * sgn(d);
    }
    return sum;
}