errorsk-4nQwBFp0LP8NpyK9WwwoT3BlbkFJyH23SKdFWR1P9Sr63sF8
最编程
2024-08-13 10:50:54
...
#coding:UTF-8
from numpy import *
from function import *
def lbfgs(fun, gfun, x0):
result = []#保留最终的结果
maxk = 500#最大的迭代次数
rho = 0.55
sigma = 0.4
H0 = eye(shape(x0)[0])
#s和y用于保存最近m个,这里m取6
s = []
y = []
m = 6
k = 1
gk = mat(gfun(x0))#计算梯度
dk = -H0 * gk
while (k < maxk):
n = 0
mk = 0
gk = mat(gfun(x0))#计算梯度
while (n < 20):
newf = fun(x0 + rho ** n * dk)
oldf = fun(x0)
if (newf < oldf + sigma * (rho ** n) * (gk.T * dk)[0, 0]):
mk = n
break
n = n + 1
#LBFGS校正
x = x0 + rho ** mk * dk
#print x
#保留m个
if k > m:
s.pop(0)
y.pop(0)
#计算最新的
sk = x - x0
yk = gfun(x) - gk
s.append(sk)
y.append(yk)
#two-loop的过程
t = len(s)
qk = gfun(x)
a = []
for i in xrange(t):
alpha = (s[t - i - 1].T * qk) / (y[t - i - 1].T * s[t - i - 1])
qk = qk - alpha[0, 0] * y[t - i - 1]
a.append(alpha[0, 0])
r = H0 * qk
for i in xrange(t):
beta = (y[i].T * r) / (y[i].T * s[i])
r = r + s[i] * (a[t - i - 1] - beta[0, 0])
if (yk.T * sk > 0):
dk = -r
k = k + 1
x0 = x
result.append(fun(x0))
return result
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