CODEWITHSUNDEEP
pythonnumpy
czhang75
czhang75

Reputation: 13

python raises syntax error when computing eigenvalues of a general matrix

I intend to plot the eigenvalue(s) of the Jacobian matrix over the range -3 ≤ μ ≤ 3 in 0.1 steps in Python.

Please see my code below: 

import numpy as np

mu = np.arange(-3,3,0.1)

J =([[0, 1],
 [-1, -mu]])

assign lambda 

lambda = np.linalg.eigvals(J)

print(lambda)

Then this showed up: "SyntaxError: invalid syntax," and it's pointing at "lambda" in the "assign lambda" line.

Then my code for plotting is 

import matplotlib.pyplot as plt 

plt.figure()
plt.plot(mu, lambda, 's') 
plt.xlabel('mu')
plt.ylabel('Eigenvalue')
plt.show()

Another "SyntaxError: invalid syntax" showed up, pointing at the "lambda" in this section.

I've also tried to get rid of the "assign lambda" line but still didn't work. This kind of error has happened before when I try to define a function or parameter.

Could anyone please take a look and help me? I am very new to Python.

Thank you very much!

Upvotes: 1

Views: 328

Answers (2)

Sheldore
Sheldore

Reputation: 39072

You are trying to vectorise mu which is not the correct way in your code. You can simply use a for loop

import numpy as np
import matplotlib.pyplot as plt 

mu = np.arange(-3,3,0.1)
lambda_list = []

for i in mu:
    J = [[0, 1],[-1, -i]]
    lambda_list.append(np.linalg.eigvals(J))

lambda_list = np.array(lambda_list)

plt.figure()
plt.plot(mu, lambda_list[:, 0], '-r', label='Eigenvalue 1') 
plt.plot(mu, lambda_list[:, 1], '-b', label='Eigenvalue 2') 
plt.xlabel('mu')
plt.ylabel('Eigenvalue')
plt.legend()

enter image description here

Upvotes: 1

mujjiga
mujjiga

Reputation: 16906

import numpy as np
import matplotlib.pyplot as plt 
mu = np.arange(-3,3,0.1)
e = list()

for m in mu:
    J = np.array([[0, 1], [-1, -m]])
    e.append(np.linalg.eigvals(J))

plt.figure()
plt.plot(mu, e, 's') 
plt.xlabel('mu')
plt.ylabel('Eigenvalue')
plt.show()
  • For each mu create a J
  • Calculate the eigen vectors for J and save it in list e
  • Finally plot eigen vectors in e with respect to mu

Upvotes: 0

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