[英]How do I fix a function that returns NAN?
I wanted to try to implement gradient descent by myself and I wrote this:我想尝试自己实现梯度下降,我写了这个:
# Creating random sample dataset
import random as rnd
dataset = []
for i in range(0, 500):
d_dataset = [i, rnd.randint((i-4), (i+4))]
dataset.append(d_dataset)
def gradient_descent(t0, t1, lrate, ds):
length = len(ds)
c0, c1 = 0, 0
for element in ds:
elx = element[0]
ely = element[1]
c0 += ((t0 + (t1*elx) - ely))
c1 += ((t0 + (t1*elx) - ely)*elx)
t0 -= (lrate * c0 / length)
t1 -= (lrate * c1 / length)
return t0, t1
def train(t0, t1, lrate, trainlimit, trainingset):
k = 0
while k < trainlimit:
new_t0, new_t1 = gradient_descent(t0, t1, lrate, trainingset)
t0, t1 = new_t0, new_t1
k += 1
return t0, t1
print(gradient_descent(20, 1, 1, dataset))
print(train(0, 0, 1, 10000, dataset))
Whenever I run this, I get a somewhat normal output from the gradient_descent()
but I get (nan, nan)
from the train()
function.每当我运行它时,我都会从gradient_descent()
得到一个有点正常的输出,但我从train()
函数得到(nan, nan)
。 I tried running train
with the input (0, 0, 1, 10, dataset)
and I get this value (-4.705770241957691e+46, -1.5670167612541557e+49)
, which seems very wrong.我尝试使用输入(0, 0, 1, 10, dataset)
运行train
并得到这个值(-4.705770241957691e+46, -1.5670167612541557e+49)
,这似乎非常错误。
Please tell me what I'm doing wrong and how to fix this error.请告诉我我做错了什么以及如何解决这个错误。 Sorry if this has been asked before but I couldn't find any answers on how to fix nan error.抱歉,如果之前有人问过这个问题,但我找不到关于如何修复 nan 错误的任何答案。
When calling print(train(0, 0, 1, 10000, dataset))
, the values returned by gradient_descent(t0, t1, lrate, trainingset)
are increasing in every iteration of the while
-loop.当调用print(train(0, 0, 1, 10000, dataset))
,由gradient_descent(t0, t1, lrate, trainingset)
返回的值在while
循环的每次迭代中都在增加。 When they become larger than the maximum value allowed for float
, they will automatically be converted to float('inf')
, a float
representing infinity.当它们变得大于float
允许的最大值时,它们将自动转换为float('inf')
,一个表示无穷大的float
。 Check this maximum value on your system with sys.float_info.max
:使用sys.float_info.max
检查系统上的sys.float_info.max
:
import sys
print(sys.float_info.max)
However, your function gradient_descent()
can't handle infinite values, which you can verify with the following call to your function:但是,您的函数gradient_descent()
无法处理无限值,您可以通过以下对您的函数的调用来验证:
gradient_descent(float('inf'), float('inf'), 1, dataset)
The problem here are the following two lines in gradient_descent()
, which are not well defined for t0
and t1
being infinite:这里的问题是gradient_descent()
中的以下两行,它们没有很好地定义t0
和t1
是无限的:
c0 += ((t0 + (t1*elx) - ely))
c1 += ((t0 + (t1*elx) - ely)*elx)
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