matlab 优化方法中求最小值，使用非精确搜索获取步长、最速下降获取方向_course

老师布置了这样的 <br></br>  我在matlab里面写，，最后一直迭代不出来。。 <br></br>  <br></br>  <br></br>  <br></br>  <br></br> 代码是这样的。。不怎么用matlab，求指教。。 <br></br> ``` clear; clc; x_k = [0; 0]; z = 1e-4; syms f(x_1, x_2); syms g(x_1, x_2); syms l(y); syms m(y); f = vpa(100 * (x_1 ^ 2 - x_2) ^ 2 + (x_1 - 1) ^ 2, 20); %原函数 g = vpa([diff(f, x_1); diff(f, x_2)], 20); %导数 c_1 = 0.1; c_2 = 0.5; y = 1; f_k = vpa(subs(f, [x_1; x_2], x_k), 20) g_k = vpa(subs(g, [x_1; x_2], x_k), 20) x_kk = vpa(x_k - y * g_k, 20); f_kk = vpa(subs(f, [x_1; x_2], x_kk), 20) g_kk = vpa(subs(g, [x_1; x_2], x_kk), 20) while norm(g_kk, 2) >= z getStep = 1; a = 0; b = inf; y = 1; while getStep if f_k - f_kk >= - c_1 * y * g_k' * (-g_k) if g_kk' * (-g_k) >= c_2 * g_k' * (-g_k) getStep = 0 else a = y; y = vpa(min(2 * y, (y + b) / 2), 20) x_kk = vpa(x_k - y * g_k, 20); f_kk = vpa(subs(f, [x_1; x_2], x_kk), 20) g_kk = vpa(subs(g, [x_1; x_2], x_kk), 20) end else b = y; y = vpa((a + y) / 2, 20) x_kk = vpa(x_k - y * g_k, 20); f_kk = vpa(subs(f, [x_1; x_2], x_kk), 20) g_kk = vpa(subs(g, [x_1; x_2], x_kk), 20) end end f_k = f_kk; g_k = g_kk; x_kk = vpa(x_k - y * g_k, 20); f_kk = vpa(subs(f, [x_1; x_2], x_kk), 20) g_kk = vpa(subs(g, [x_1; x_2], x_kk), 20) end ``` <br></br>