CODEWITHSUNDEEP
pythonpython-3.xtypeerror
user2281223
user2281223

Reputation: 41

TypeError: __getitem__() takes exactly 2 arguments (2 given) TypeError? (Python 3)

I have the following function defined:

def eigval(matrix):
    a = matrix[0, 0]
    b = matrix[0, 1]
    c = matrix[1, 0]
    d = matrix[1, 1]
    c1 = (a + d) + sqrt((4 * b * c) + ((a - d)**2))
    c2 = (a + d) - sqrt((4 * b * c) + ((a - d)**2))
    return c1 / 2, c2 / 2

It is created to find the eigenvalues of a 2 X 2 matrix. I am using it to iteratively run the Jacobi algorithm on a matrix. The matrix passed in is a dictionary that uses tuples as keys to represent the position and floats as values. This function will work fine for about 6 iterations, but then I will get a:

TypeError: __getitem__() takes exactly 2 arguments (2 given)

on the first line of the block (the one with the a).

I am completely confused by this because like I said, it works fine for about 6 runs and then stops.

EDIT: Here's a function that creates the kind of matrix I would pass in: (Given that the matrix will be different for each iteration)

def create():
    matrix = {}
    matrix[0, 0] = 2
    matrix[0, 1] = 1
    matrix[1, 0] = 1
    matrix[1, 1] = 2
    return matrix

Any help is greatly appreciated! (P.S. first post here)

Upvotes: 4

Views: 2107

Answers (1)

sn6uv
sn6uv

Reputation: 609

Your matrix is a dict using tuples as keys, this is probably not what you want to do.

Try using nested lists:

from math import sqrt

def create():
    matrix = [[1, 2], [1, 2]]
    return matrix

def eigval(matrix):
    a = matrix[0][0]
    b = matrix[1][0]
    c = matrix[0][1]
    d = matrix[1][1]
    c1 = (a + d) + sqrt((4 * b * c) + ((a - d)**2))
    c2 = (a + d) - sqrt((4 * b * c) + ((a - d)**2))
    return [c1 / 2, c2 / 2]

>>> m = create() 
>>> eigval(m)
[3.0, 0.0]

Or alternatively use numpy:

import numpy

def eigval(matrix):
    a = matrix[0, 0]
    b = matrix[1, 0]
    c = matrix[0, 1]
    d = matrix[1, 1]
    c1 = (a + d) + sqrt((4 * b * c) + ((a - d)**2))
    c2 = (a + d) - sqrt((4 * b * c) + ((a - d)**2))
    return numpy.array([c1 / 2, c2 / 2])

>>> m = numpy.array([[1, 2], [1, 2]])
>>> m
array([[1, 2],
       [1, 2]])
>>> eigvalues, eigvectors = numpy.linalg.eig(m)
>>> eigvalues
array([ 0.,  3.])

>>> eigval(m)
array([ 3.,  0.])

Upvotes: 1

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