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

1. My code opens up a text file containing a matrix:
   1 2
3 4
   and places it in list x as integers.

2. The list x is then converted into an array a.

3. The eigenvalues of a are placed in l and the eigenvectors are placed in v.

4. I then want to take the exp(a) and place it in another array exponent.

5. Then I create an identity matrix L of whatever length l is.

6. 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?

Answer 1

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) 

?

Answer 2

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__'