CVXPY matrix multipication in Python 2.7

Question

I'm using the CVXPY code here. I want to run it on Python 2.7 instead of Python 3. The operator @ seems to work on Python 3. To make it work for python 2.7, I revised the code as

import cvxpy as cp
import numpy as np

n = 3
p = 3
np.random.seed(1)
C = np.random.randn(n, n)
A = []
b = []
for i in range(p):
   A.append(np.random.randn(n, n))
b.append(np.random.randn())

X = cp.Variable((n,n), symmetric=True)
# The operator >> denotes matrix inequality.
constraints = [X >> 0] 
prob = cp.Problem(cp.Minimize(np.matmul(C,X)), constraints)
prob.solve()

where I used numpy.matmul instead of @. However, it gives me this error "ValueError: matmul: Input operand 1 does not have enough dimensions"

My question is how to run this code here successfully in python 2.7 (instead of Python 3).

Answer 1

You need to use cvxpy operators on cvxpy variables, in other words you can't do np.matmul with a cvxpy variable. You can just use the * operator. cvxpy will treat this as matrix multiplication. Try this,

C = np.random.randn(2, n)
C * X

and you'll get:

Expression(AFFINE, UNKNOWN, (2, 3))