Scilab Function
Last update : 5/9/2006

sirs - the susceptible-infected-rescued-susceptible (SIRS) model

### Calling Sequence

  `inf = sirs(a,b,N,T,N0,Ti,Tr,P)`

### Parameters

- `a` : row vector of the numbers of the tail nodes of the graph (its size is the number of edges of the graph)
- `b` : row vector of the numbers of the head nodes of the graph (its size is the number of edges of the graph)
- `N` : the node number of the SIRS model
- `T` : the epidemic time step
- `N0` : the initial infected node
- `Ti` : the infected state holding time, then the node will change its status to refractory state
- `Tr` : the refractory state holding time, then the node will change its status to suspectible state
- `P` : the infected probability
- `inf` : row vector of the infected fraction of the graph(its size is the time step)

### Description

  sirs calculates the infected fraction every time step for the SIRS epidemic process. Note when the TR is large enough, SIRS is the SIR epidemic process.

### Examples

    	  [a b]=ba(6,4,9994);
    	  inf=sirs(a,b,10000,1000,1000,5,3,1);
    	  t=[1:1000];
    	  plot2d(t,inf(t));

### See Also

`sis` ,

### Authors

  Wubo