Since each compartment identifies an atomic condition it is natural to imagine rules described as trees of compartments.
A compartment tree identify and ordered and disjoint set of conditions that needs to be satisfied to allow status transition (it allows describing an OR logic).
To implement such behaviour we implemented a ConditionalComposition compartment that allows to describe branching. Let’s call it CC.
CC evaluate a guard compartment and, depending from the result it gets evaluate (True or False) move to the evaluation of one of its two child compartments.
In the code below is shown the formulation of a model implementing conditional compartment composition.
The rule Susceptible->Infected is implemented using three NodeStochastic compartments chained as follows:
- If the node n is Susceptible
- c1: if at least a neighbor of the actual node is Infected, with probability 0.5 evaluate compartment c2 else evaluate compartment c3
- c2: with probability 0.2 allow the transition to the Infected state
- c3: with probability 0.1 allow the transition to the Infected state
Indeed, heterogeneous compartment types can be mixed to build more complex scenarios.
import networkx as nx import ndlib.models.ModelConfig as mc import ndlib.models.CompositeModel as gc import ndlib.models.compartments.NodeStochastic as ns import ndlib.models.compartments.ConditionalComposition as cif # Network generation g = nx.erdos_renyi_graph(1000, 0.1) # Composite Model instantiation model = gc.CompositeModel(g) # Model statuses model.add_status("Susceptible") model.add_status("Infected") # Compartment definition c1 = ns.NodeStochastic(0.5, "Infected") c2 = ns.NodeStochastic(0.2) c3 = ns.NodeStochastic(0.1) # Conditional Composition cc = cif.ConditionalComposition(c1, c2, c3) # Rule definition model.add_rule("Susceptible", "Infected", cc) # Model initial status configuration config = mc.Configuration() config.add_model_parameter('fraction_infected', 0.1) # Simulation execution model.set_initial_status(config) iterations = model.iteration_bunch(100)