TypeError: can only be called with ndarray object

[Wendell]

Hi!

When I tried the example code:

import cvxpy as cp 

import numpy as np 

# Generate data. 

m = 20 

n = 15 

np.random.seed(1) 

A = np.random.randn(m, n) 

b = np.random.randn(m) 

# Define and solve the CVXPY problem. 

x = cp.Variable(n) 

cost = cp.sum_squares(A @ x - b) 

prob = cp.Problem(cp.Minimize(cost)) 

prob.solve() 

# Print result. 

print("\nThe optimal value is", prob.value) 

print("The optimal x is") 

print(x.value) 

print("The norm of the residual is ", cp.norm(A @ x - b, p=2).value)

I received an error: 

File "D:\anaconda\envs\lib\site-packages\cvxpy\cvxcore\python\canonInterface.py", line 348, in get_problem_matrix

    tensor_J[param_id][i]*constr_length)

TypeError: can only be called with ndarray object

How to solve this? I