Python 向随机梯度下降中添加扩展成本的目的是什么
我正试图实现一个基于斯坦福大学第一次分配给cs224n的脚手架的SGD。实现是用python实现的。脚手架如下:Python 向随机梯度下降中添加扩展成本的目的是什么,python,neural-network,gradient-descent,Python,Neural Network,Gradient Descent,我正试图实现一个基于斯坦福大学第一次分配给cs224n的脚手架的SGD。实现是用python实现的。脚手架如下: def load_saved_params(): '''A helper function that loads previously saved parameters and resets iteration start.''' return st, params, state #st = starting iteration def save_params(iter, para
def load_saved_params():
'''A helper function that loads previously saved parameters and resets
iteration start.'''
return st, params, state #st = starting iteration
def save_params(iter, params):
'''saves the parameters'''
现在是主函数(我已经用多个散列符号跟随了相关语句)
就我的目的而言,我没有使用成本。但是代码中expcost的目的是什么。在什么情况下可以使用它?为什么在修改成本函数计算的成本时使用它?如果您注意到,
expcost
仅用于打印成本。这只是一种平滑成本函数的方法,因为它可以从一个批次跳到另一个批次,尽管模型的改进完全有意义。非常感谢。如果明天我还没有一个答案能指出其他更密切的用途,我会接受这个答案
def sgd(f, x0, step, iterations, postprocessing=None, useSaved=False,
PRINT_EVERY=10):
""" Stochastic Gradient Descent
Implement the stochastic gradient descent method in this function.
Arguments:
f -- the function to optimize, it should take a single
argument and yield two outputs, a cost and the gradient
with respect to the arguments
x0 -- the initial point to start SGD from
step -- the step size for SGD
iterations -- total iterations to run SGD for
postprocessing -- postprocessing function for the parameters
if necessary. In the case of word2vec we will need to
normalize the word vectors to have unit length.
PRINT_EVERY -- specifies how many iterations to output loss
Return:
x -- the parameter value after SGD finishes
"""
# Anneal learning rate every several iterations
ANNEAL_EVERY = 20000
if useSaved:
start_iter, oldx, state = load_saved_params()
if start_iter > 0:
x0 = oldx
step *= 0.5 ** (start_iter / ANNEAL_EVERY)
if state:
random.setstate(state)
else:
start_iter = 0
x = x0
if not postprocessing:
postprocessing = lambda x: x
expcost = None ######################################################
for iter in xrange(start_iter + 1, iterations + 1):
# Don't forget to apply the postprocessing after every iteration!
# You might want to print the progress every few iterations.
cost = None
### END YOUR CODE
if iter % PRINT_EVERY == 0:
if not expcost:
expcost = cost
else:
expcost = .95 * expcost + .05 * cost ########################
print "iter %d: %f" % (iter, expcost)
if iter % SAVE_PARAMS_EVERY == 0 and useSaved:
save_params(iter, x)
if iter % ANNEAL_EVERY == 0:
step *= 0.5
return x