# Count Down¶

Count Down compartments are used to evaluate time related deterministic events attached to network nodes.

Consider the transition rule Susceptible->Infected that has an incubation period of t iterations.

Such rule can be described by a simple compartment that models Count Down behaviors. Let’s call il CD.

The rule will take as input the initial node status (Susceptible), the final one (Infected) and the CD compartment. CD will thus require a countdown name (cn) and the number of iterations (t) before activation.

During each rule evaluation, given a node n

• if the actual status of n equals the rule initial one
• if the node does not have an associated countdown cn initialize it to t
• else
• if cn(t) > t decrement cn(t)
• if cn(t) <= t then CD is considered satisfied and the status of n changes from initial to final.

## Parameters¶

Name Value Type Default Mandatory Description
name string None True Count Down name
iterations int None True Duration

## Example¶

In the code below is shown the formulation of a model using CountDown compartments.

The compartment, c1, is used to implement the transition rule Susceptible->Infected. It requires activates after 10 iteration.

import networkx as nx
import ndlib.models.ModelConfig as mc
import ndlib.models.CompositeModel as gc
import ndlib.models.compartments.CountDown as cd

# Network generation
g = nx.erdos_renyi_graph(1000, 0.1)

# Composite Model instantiation
model = gc.CompositeModel(g)

# Model statuses

# Compartment definition
c1 = cd.CountDown("incubation", iterations=10)

# Rule definition