/* mortgage payment */
mpay(rate, yterm, amount)
{
        local a, m, r, p;

        m = yterm * 12.0;
        r = (rate / 100.0) / 12;
        
        if (r == 0.0)
        {
                p = amount / m;
        }
        else
        {
                a = 1.0 + r;
                p = (amount * a ^ m * r) / (a ^ m - 1);
        }
        
        return(p);
}