Python 索引 4 超出轴 1 的范围，大小为 4 代码为双和
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index 4 is out of bounds for axis 1 with size 4 Code with Double Sum
提问by Shaun
Hi I have the following function which produces an out of bounds error:
嗨，我有以下函数会产生越界错误：
import numpy as np
import pylab as plt
import scipy
import math
import sympy as sy
T = sy.Symbol('T')
rho = sy.Symbol('rho')
g_T = [1,T,T**2,T*sy.log(T),T**2*sy.log(T)]
g_rho = [1,rho,rho**2,rho*sy.log(rho),rho**2*sy.log(rho)]
g_T_np = np.asarray(g_T)
g_rho_np = np.asarray(g_rho)
c = np.loadtxt("c_test.txt")
def F(T,rho):
ret = 0
for n in xrange(1,5):
for m in xrange(1,6):
inner= c[n,m]*g_T_np*g_rho_np
ret += inner
return ret
print F(T,rho)
where the .txt file is like this:
其中 .txt 文件是这样的：
-0.529586 -0.000208559 -3.36563E-09 2.29441E-05
2.22722E-06 -0.00014526 -2.48888E-09 1.89488E-05
-6.26662E-05 0.000421028 6.17407E-09 -5.14488E-05
0.09977346 -0.000622051 -8.56485E-09 7.49956E-05
-0.01437627 -9.86754E-05 -1.59808E-09 1.22574E-05
The full error displayed is:
显示的完整错误是：
Traceback (most recent call last):File "EOS_test.py", line 38, in <module> print F(T,rho) File "EOS_test.py", line 31, in F inner=c[n,m]*g_T_np*g_rho_np IndexError: index 4 is out of bounds for axis 1 with size 4
Traceback (most recent call last):File "EOS_test.py", line 38, in <module> print F(T,rho) File "EOS_test.py", line 31, in F inner=c[n,m]*g_T_np*g_rho_np IndexError: index 4 is out of bounds for axis 1 with size 4
How can I solve this error?
我该如何解决这个错误？
采纳答案by pdowling
Numpy uses 0-based indexing. From the looks of it you are indexing the array from 1 (2nd position) to 4 (5th position), which is of course out of bounds for the array you are working with. The same is true for the second axis.
Numpy 使用基于 0 的索引。从它的外观来看，您正在将数组从 1（第 2 位）索引到 4（第 5 位），这当然超出了您正在使用的数组的范围。对于第二个轴也是如此。
Secondly, you've mixed up your axes:
其次，你混淆了你的轴：
- The first axis (0) is the index of the selected row (0 to 5)
- the second axis indexes the column, i.e. the value inside a row (indexed 0 to 4)
- 第一个轴 (0) 是所选行的索引（0 到 5）
- 第二个轴索引列，即行内的值（索引为 0 到 4）
This should work:
这应该有效：
def F(T,rho):
ret = 0
for n in range(5):
for m in range(4):
inner= c[n,m]*g_T_np*g_rho_np
ret += inner
return ret
回答by Scott Mermelstein
Your problem is in setting your xranges.
您的问题在于设置您的xranges。
Python lists (and np arrays) are 0 indexed, so you don't want the indices [1,2,3,4,5] and [1,2,3,4,5,6], but instead want [0,1,2,3,4] and [0,1,2,3,4,5][0,1,2,3] and [0,1,2,3,4].
Python 列表（和 np 数组）的索引为 0，因此您不想要索引 [1,2,3,4,5] 和 [1,2,3,4,5,6]，而是想要[0 ,1,2,3,4] 和 [0,1,2,3,4,5][0,1,2,3] 和 [0,1,2,3,4]。
Setting up your for loops like this would solve your problem:
像这样设置 for 循环可以解决您的问题：
for n in xrange(0,4):
for m in xrange(0,5):
Or, you can take advantage of xrange's default starting point, and simply list one parameter:
或者，您可以利用 xrange 的默认起点，并简单地列出一个参数：
for n in xrange(4):
for m in xrange(5):
Also, for a "more pythonic" solution, instead of having nested for loops, look up how to iterate over an ndarray. The docsgive this example:
此外，对于“更 Pythonic”的解决方案，不要嵌套 for 循环，而是查找如何迭代 ndarray。该文档举这个例子：
it = np.nditer(c, flags=['f_index'])
while not it.finished:
inner= c[it[0]]*g_T_np*g_rho_np
ret += inner
it.iternext()
This avoids the whole issue of needing to know the size of the array you're importing, and is therefore much more robust.
这避免了需要知道您正在导入的数组大小的整个问题，因此更加健壮。
Edit: As pdowling mentioned in his answer, the range numbers should be 4 and 5. I had left 5 and 6 in my aswer, and have now changed that.
编辑：正如 pdowling 在他的回答中提到的，范围数字应该是 4 和 5。我在我的答案中留下了 5 和 6，现在已经改变了。
