cirq.plot_density_matrix outputs buggy plots (abstract art) and doesn't scale with number of qubits.

[tanujkhattar]

Description of the issue
cirq.plot_density_matrix is buggy and output's random plots (tested in a colab) and would also doesn't scale well with number of qubits.

My guess is that this due to the magic numbers hardcoded in the code, which should be changed and computed on the fly based on the size of the density matrix.

Cirq/cirq-core/cirq/vis/density_matrix.py

Line 39 in 09a4667

_half_cell_size_after_padding = (1 / 1.1) * 0.5

How to reproduce the issue

import cirq
cirq.plot_density_matrix(cirq.testing.random_density_matrix(dim=4, random_state = 12345))

Cirq version
0.14.0.dev20220105215702

cc @AnimeshSinha1309

[dabacon]

It does look like some sort of abstract art, though :)

[tanujkhattar]

@dabacon Updated the title to better reflect what's happening :P

[AnimeshSinha1309]

I have no idea how all the multiply operations were written as divide, I had made the mistake but I remember that things were working last I checked. Anyways, fixed this, please lemme know if stuff is working now. Not sure if adding a test here would help, maybe I can add that radius of any circle should not be more than 1 and same with with length of any line.