quantum.gates.CNOT does not appear to work as advertised

[Connor Connor]

The doc string of sympy.physics.quantum.gate.CNOT contains:

"""

Two qubit controlled-NOT.

This gate performs the NOT or X gate on the target qubit if the control

qubits all have the value 1.    

"""

Which I find slightly confusing.  Does this gate work on only two qubits as the

first line indicates, or two sets of qubits, the control bits and the singleton

target?

It *appears* that it only works on two qubits: a single control and a single

target.  However the method signatures and docs seem to indicate that it is capable of

more.  I tried delving into the code, but got tangled up, so I thought I would

just ask here instead.

There is example code below.  Can any one tell me if I'm reading the docs wrong, or if CNOT is broken?

from sympy import Matrix

from sympy.physics.quantum import gate

from sympy.physics.quantum.qubit import Qubit

from sympy.physics.quantum.qapply import qapply 

q = Qubit('111')

cn = gate.CNOT(2, 1, 0)

print(qapply(cn*q)) # |101> but I expected |011>, or possibly |110>

v = Matrix([0, 0, 0, 0, 0, 0, 0, 1])

## This matrix is equivalent to what the documentation implies CNOT(2, 1, 0) is

g = Matrix([[1, 0, 0, 0, 0, 0, 0, 0],

            [0, 1, 0, 0, 0, 0, 0, 0],

            [0, 0, 1, 0, 0, 0, 0, 0], 

            [0, 0, 0, 0, 0, 0, 0, 1], 

            [0, 0, 0, 0, 1, 0, 0, 0], 

            [0, 0, 0, 0, 0, 1, 0, 0], 

            [0, 0, 0, 0, 0, 0, 1, 0], 

            [0, 0, 0, 1, 0, 0, 0, 0]])

print(repr(g*v)) # 0,0,0,1,0,0,0,0 which is equivalent to |011>