# FIXME y = 0.2*x_1^2 + 2*x2^2 测试
eta = 2 # 比之前的大，但是效果很好，不会发散
def adagrad_2d(x1, x2, s1, s2):
g1, g2, eps = 0.2*x1, 4*x2, 1e-6
s1 += g1**2
s2 += g2**2
x1 -= eta/math.sqrt(s1+eps) * g1
x2 -= eta/math.sqrt(s2+eps) * g2
return x1, x2, s1, s2
def fx(x1, x2):
return 0.1*x1**2 + 2*x2**2
d2l.plt.figure(figsize=(15,5)) # 设置图片大小7
d2l.show_trace_2d(fx, d2l.train_2d(adagrad_2d))
# 手动写一个
features, labels = d2l.get_data_ch7()
def inin_adagrad_states():
s_w = nd.zeros((features.shape[1], 1))
s_b = nd.zeros(1)
return (s_w, s_b)
def adagrad(params, states, hyperparams):
eps = 1e-6
for p,s in zip(params, states):
s[:] += p.grad.square()
p[:] -= hyperparams['lr'] * p.grad / (s+eps).sqrt()
def rmsprop_2d(x1, x2, s1, s2):
g1, g2, eps = 0.2 * x1, 4 * x2, 1e-6
s1 = gamma * s1 + (1 - gamma) * g1**2
s2 = gamma * s2 + (1 - gamma) * g2**2
x1 -= eta / math.sqrt(s1 + eps) * g1
x2 -= eta / math.sqrt(s2 + eps) * g2
return x1, x2, s1, s2
def f_2d(x1, x2):
return 0.1 * x1**2 + 2 * x2**2
eta, gamma = 0.4, 0.9
d2l.show_trace_2d(f_2d, d2l.train_2d(rmsprop_2d))
#7.6.2-从零开始实现
features, labels = d2l.get_data_ch7()
def init_rmsprop_states():
s_w = nd.zeros((features.shape[1], 1))
s_b = nd.zeros(1)
return (s_w, s_b)
def rmsprop(params, states, hyperparams):
gamma, eps = hyperparams['gamma'], 1e-6
for p, s in zip(params, states):
s[:] = gamma * s + (1 - gamma) * p.grad.square()
#7.4-动量法
#7.4.1-梯度下降的问题
#%matplotlib inline
import d2lzh as d2l
from mxnet import nd
eta = 0.4
def f_2d(x1, x2):
return 0.1 * x1 ** 2 + 2 * x2 ** 2
def gd_2d(x1, x2, s1, s2):
return (x1-eta*0.2*x1, x2-eta*4*x2, 0, 0)
d2l.show_trace_2d(f_2d, d2l.train_2d(gd_2d))
#学习率调大，自变量在竖直方向上不断越过最优解并逐渐发散
eta = 0.6
d2l.show_trace_2d(f_2d, d2l.train_2d(gd_2d))
#7.4.2-动量法
def momentum_2d(x1, x2, v1, v2):
v1 = gamma * v1 + eta * 0.2 * x1
v2 = gamma * v2 + eta * 4* x2
return x1-v1, x2-v2, v1, v2
eta, gamma = 0.4, 0.5
d2l.show_trace_2d(f_2d, d2l.train_2d(momentum_2d))
eta =0.6
d2l.show_trace_2d(f_2d, d2l.train_2d(momentum_2d))