Magic Cuts¶

This example explores a system of three fully connected elements \(A\), \(B\) and \(C\), which follow the logic of the Rule 110 cellular automaton. The point of this example is to highlight an unexpected behaviour of system cuts, that the minimum information partition of a system can result in new concepts being created.

First let’s create the the Rule 110 network, with all nodes OFF in the current state.

>>> import pyphi
>>> network = pyphi.examples.rule110_network()
>>> state = (0, 0, 0)

Next, we want to identify the spatial scale and main complex of the network:

>>> macro = pyphi.macro.emergence(network, state)
>>> macro.emergence
-1.35708

Since the emergence value is negative, there is no macro scale which has greater integrated information than the original micro scale. We can now analyze the micro scale to determine the main complex of the system:

>>> main_complex = pyphi.compute.main_complex(network, state)
>>> subsystem = main_complex.subsystem
>>> subsystem
Subsystem((n0, n1, n2))
>>> main_complex.phi
1.35708

The main complex of the system contains all three nodes of the system, and it has integrated information \(\Phi = 1.35708\). Now that we have identified the main complex of the system, we can explore its conceptual structure and the effect of the MIP.

>>> constellation = main_complex.unpartitioned_constellation

There two equalivalent cuts for this system; for concreteness we sever all connections from elements \(A\) and \(B\) to \(C\).

>>> cut = pyphi.models.Cut(severed = (0, 1), intact = (2,))
>>> cut_subsystem = pyphi.Subsystem(network, state, range(network.size), cut)
>>> cut_constellation = pyphi.compute.constellation(cut_subsystem)

Lets investigate the concepts in the unpartitioned constellation,

>>> [concept.mechanism for concept in constellation]
[(0,), (1,), (2,), (0, 1), (0, 2), (1, 2)]
>>> [concept.phi for concept in constellation]
[0.125, 0.125, 0.125, 0.499999, 0.499999, 0.499999]
>>> sum(_)
1.8749970000000002

and also the concepts of the partitioned constellation.

>>> [concept.mechanism for concept in cut_constellation]
[(0,), (1,), (2,), (0, 1), (1, 2), (0, 1, 2)]
>>> [concept.phi for concept in cut_constellation]
[0.125, 0.125, 0.125, 0.499999, 0.266666, 0.333333]
>>> sum(_)
1.4749980000000003

The unpartitioned constellation includes all possible first and second order concepts, but there is no third order concept. After applying the cut, and severing the connections from \(A\) and \(B\) to \(C\), a third order concept is created in the partitioned constellation. A new concept is created as a result of the cut, but there is also a concept destroyed |A,B| and the overall amount of \(\varphi\) in the system decreases from \(1.875\) to \(1.475\).

Lets explore the concept which was created to determine why it does not exist in the unpartitioned constellation and what changed in the partitioned constellation.

>>> subsystem = main_complex.subsystem
>>> ABC = subsystem.node_indices
>>> subsystem.cause_info(ABC, ABC)
0.749999
>>> subsystem.effect_info(ABC, ABC)
1.875

The mechanism has cause and effect power over the system, so it must be that this power is reducible.

>>> mice_cause = subsystem.core_cause(ABC)
>>> mice_cause.phi
0.0
>>> mice_effect = subsystem.core_effect(ABC)
>>> mice_effect.phi
0.624999

The reason ABC does not exist as a concept is that its cause is reducible. Looking at the TPM of the system, there are no possible states with two of the elements set to OFF. This means that knowing two elements are OFF is enough to know that the third element must also be OFF, and thus the third element can always be cut from the concept without a loss of information. This will be true for any purview, so the cause information is reducible.

>>> BC = (1, 2)
>>> A = (0,)
>>> repertoire = subsystem.cause_repertoire(ABC, ABC)
>>> cut_repertoire = subsystem.cause_repertoire(BC, ABC) * subsystem.cause_repertoire(A, ())
>>> pyphi.utils.hamming_emd(repertoire, cut_repertoire)
0.0

Next, lets look at the cut subsystem to understand how the new concept comes into existence.

>>> ABC = (0, 1, 2)
>>> C = (2,)
>>> AB = (0, 1)

The cut applied to the subsystem severs the connections from \(A\) and \(B\) to \(C\). In this circumstance, knowing \(A\) and \(B\) do not tell us anything about the state of \(C\), only the past state of \(C\) can tell us about the future state of \(C\). Here, past_tpm[1] gives us the probability of C being ON in the next state, while past_tpm[0] would give us the probability of C being OFF.

>>> C_node = cut_subsystem.indices2nodes(C)[0]
>>> C_node.tpm[1].flatten()
array([ 0.5 ,  0.75])

This states that A has a 50% chance of being ON in the next state if it currently OFF, but a 75% chance of being ON in the next state if it is currently ON. Thus unlike the unpartitioned case, knowing the current state of C gives us additional information over and above knowing A and B.

>>> repertoire = cut_subsystem.cause_repertoire(ABC, ABC)
>>> cut_repertoire = cut_subsystem.cause_repertoire(AB, ABC) * cut_subsystem.cause_repertoire(C, ())
>>> pyphi.utils.hamming_emd(repertoire, cut_repertoire)
0.500001

With this partition, the integrated information is \(\varphi = 0.5\), but we must check all possible partitions to find the MIP.

>>> cut_subsystem.core_cause(ABC).purview
(0, 1, 2)
>>> cut_subsystem.core_cause(ABC).phi
0.333333

It turns out that the MIP is

\[\frac{AB}{[\,]} \times \frac{C}{ABC}\]

and the integrated information of ABC is \(\varphi = 1/3\).

Note: In order for a new concept to be created by a cut, there must be a within mechanism connection severed by the cut.

In the previous example, the MIP created a new concept, but the amount of \(\varphi\) in the constellation still decreased. This is not always the case. Next we will look at an example of system whoes MIP increases the amount of \(\varphi\). This example is based on a five node network which follows the logic of the Rule 154 cellular automaton. Lets first load the network,

>>> network = pyphi.examples.rule154_network()
>>> state = (1, 0, 0, 0, 0)

For this example, it is the subsystem consisting of |n0, n1, n4| that we explore. This is not the main concept of the system, but it serves as a proof of principle regardless.

>>> subsystem = pyphi.Subsystem(network, state, (0, 1, 4))

Calculating the MIP of the system,

>>> mip = pyphi.compute.big_mip(subsystem)
>>> mip.phi
0.217829
>>> mip.cut
Cut (0, 4) --//--> (1,)

This subsystem has a \(\Phi\) value of 0.15533, and the MIP cuts the connections from |n0, n4| to \(n_{1}\). Investigating the concepts in both the partitioned and unpartitioned constellations,

>>> unpartitioned_constellation = mip.unpartitioned_constellation
>>> [concept.mechanism for concept in unpartitioned_constellation]
[(0,), (1,), (0, 1)]
>>> [concept.phi for concept in unpartitioned_constellation]
[0.25, 0.166667, 0.178572]
>>> sum([concept.phi for concept in unpartitioned_constellation])
0.5952390000000001

The unpartitioned constellation has mechanisms \(n_{0}\), \(n_{1}\) and \(n_{0}n_{1}\) with \(\sum\varphi = 0.595239\).

>>> partitioned_constellation = mip.partitioned_constellation
>>> [concept.mechanism for concept in partitioned_constellation]
[(0, 1), (0,), (1,)]
>>> [concept.phi for concept in partitioned_constellation]
[0.214286, 0.25, 0.166667]
>>> sum([concept.phi for concept in partitioned_constellation])
0.630953

The unpartitioned constellation has mechanisms \(n_{0}\), \(n_{1}\) and \(n_{0}n_{1}\) with \(\sum\varphi = 0.630953\). There are the same number of concepts in both constellations, over the same mechanisms; however, the partitioned constellation has a greater \(\varphi\) value for the concept \(n_{0}n_{1}\), resulting in an overall greater \(\sum\varphi\) for the MIP constellation.

Although situations described above are rare, they do occur, so one must be careful when analyzing the integrated information of physical systems not to dismiss the possibility of partitions creating new concepts or increasing the amount of \(\varphi\); otherwise, an incorrect main complex may be identified.