What does it mean to have an index to scalar variable error? python

Question

import numpy as np

with open('matrix.txt', 'r') as f:
    x = []
    for line in f:
        x.append(map(int, line.split()))
f.close()

a = array(x)

l, v = eig(a)

exponent = array(exp(l))

L = identity(len(l))

for i in xrange(len(l)):
    L[i][i] = exponent[0][i]

print L

My code opens up a text file containing a matrix:
1 2
3 4
and places it in list x as integers.
The list x is then converted into an array a.
The eigenvalues of a are placed in l and the eigenvectors are placed in v.
I then want to take the exp(a) and place it in another array exponent.
Then I create an identity matrix L of whatever length l is.
My for loop is supposed to take the values of exponent and replace the 1's across the diagonal of the identity matrix but I get an error saying

invalid index to scalar variable.

What is wrong with my code?

post the traceback please :)

IT Ninja
– IT Ninja

2012-11-27 22:43:40 +00:00
Commented Nov 27, 2012 at 22:43 — IT Ninja
– IT Ninja, Commented Nov 27, 2012 at 22:43

NPE · Accepted Answer · 2012-11-27 22:51:36Z

31

exponent is a 1D array. This means that exponent[0] is a scalar, and exponent[0][i] is trying to access it as if it were an array.

Did you mean to say:

L = identity(len(l))
for i in xrange(len(l)):
    L[i][i] = exponent[i]

or even

L = diag(exponent)

?

edited Nov 27, 2012 at 22:51

answered Nov 27, 2012 at 22:45

NPE

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Comments

Akavall · Accepted Answer · 2013-09-19 20:36:37Z

IndexError: invalid index to scalar variable happens when you try to index a numpy scalar such as numpy.int64 or numpy.float64. It is very similar to TypeError: 'int' object has no attribute '__getitem__' when you try to index an int.

>>> a = np.int64(5)
>>> type(a)
<type 'numpy.int64'>
>>> a[3]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: invalid index to scalar variable.
>>> a = 5
>>> type(a)
<type 'int'>
>>> a[3]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object has no attribute '__getitem__'

@hoangtran, to fix it you have to fix your code. There is no meaningful result that 5[2] can give you. Somewhere, you think that an array has 1 more dimension than it really does.

nbro · Accepted Answer · 2020-04-07 19:46:56Z

2

In my case, I was getting this error because I had an input named x and I was creating (without realizing it) a local variable called x. I thought I was trying to access an element of the input x (which was an array), while I was actually trying to access an element of the local variable x (which was a scalar).

answered Apr 7, 2020 at 19:46

nbro

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