SIS
The SIS model was introduced in 1927 by Kermack .
In this model, during the course of an epidemics, a node is allowed to change its status from Susceptible (S) to Infected (I).
The model is instantiated on a graph having a nonempty set of infected nodes.
SIS assumes that if, during a generic iteration, a susceptible node comes into contact with an infected one, it becomes infected with probability beta, than it can be switch again to susceptible with probability lambda (the only transition allowed are S→I→S).
Statuses
During the simulation a node can experience the following statuses:
Name 
Code 
Susceptible 
0 
Infected 
1 
Parameters
Name 
Type 
Value Type 
Default 
Mandatory 
Description 
beta 
Model 
float in [0, 1] 

True 
Infection probability 
lambda 
Model 
float in [0, 1] 

True 
Recovery probability 
The initial infection status can be defined via:
 percentage_infected: Model Parameter, float in [0, 1]
 Infected: Status Parameter, set of nodes
The two options are mutually exclusive and the latter takes precedence over the former.
Methods
The following class methods are made available to configure, describe and execute the simulation:
Describe
SISModel.
get_info
(self)

Describes the current model parameters (nodes, edges, status)
Returns: 
a dictionary containing for each parameter class the values specified during model configuration 
SISModel.
get_status_map
(self)

Specify the statuses allowed by the model and their numeric code
Returns: 
a dictionary (status>code) 
Execute Simulation
SISModel.
iteration
(self)

Execute a single model iteration
Returns: 
Iteration_id, Incremental node status (dictionary node>status) 
SISModel.
iteration_bunch
(self, bunch_size)

Execute a bunch of model iterations
Parameters: 
 bunch_size – the number of iterations to execute
 node_status – if the incremental node status has to be returned.

Returns: 
a list containing for each iteration a dictionary {“iteration”: iteration_id, “status”: dictionary_node_to_status}
