#/***********************************************************
#    goldsect.rb -- 黄金分割法
#***********************************************************/

def goldsect( a,  b, tolerance, f )
    r = 2 / (3 + Math::sqrt(5))

    if (a > b);  t = a;  a = b;  b = t;  end
    t = r * (b - a);  c = a + t;  d = b - t
    fc = f.call(c);  fd = f.call(d)
    while (true) 
        if (fc > fd) 
            a = c;  c = d;  fc = fd;  d = b - r * (b - a)
            if (d - c <= tolerance); return c; end
            fd = f.call(d)
        else 
            b = d;  d = c;  fd = fc;  c = a + r * (b - a)
            if (d - c <= tolerance); return d; end
            fc = f.call(c)
        end
    end
end

TEST = true
$count = 0

func = Proc.new do |x|  # 最小化する関数 
    $count = 0
    xmin = 0.314

    value = (x - xmin) * (x - xmin)
    if TEST
        printf("%4d:  f(%g) = %g\n", $count += 1, x, value)
    end
    value
end

printf("x = %g\n", goldsect(0, 1, 1e-6, func))

exit 0