Slices and index giving unintuitive results

[hassanarif87]

Hi

I am learning how to use cvxrust, it is an excellent crate.

In my example I define a 2d expression Variable use slicing / indexing into it to built constraints. I am using it to build an MPC example similar to this https://osqp.org/docs/examples/mpc.html, where the shape represents (state, N) where N is the time horizon.

    let x_init = variable((10,10));
    let x = slice(&x_init,0, 5);
    let x2 = index(&x_init, 1);

    println!("Shape of x_init: {:?}", x_init.shape());
    println!("Shape of x: {:?}", x.shape());
    println!("Shape of x2: {:?}", x2.shape());

This shows

Shape of x_init: Shape([10, 10])
Shape of x: Shape([5])
Shape of x2: Shape([])

If i create a similar example in CVXPY

x_init = cp.Variable((10,10))
x = x_init[0:5] 
x2 = x_init[1]

print(np.shape(x_init))
print(np.shape(x))
print(np.shape(x2))

I get more expected results.

(10, 10)
(5, 10)
(10,)

Secondly, the index fn allows me to index out of bounds and still returns the shape Shape([])

My questions is, is this behavior expected and I am misunderstanding the usage, or this is indeed a bug.

Hassan

Edit:
here is my attempt to transcribe the problem, its does not work https://github.com/hassanarif87/cvx_opt/blob/main/src/main.rs