Doubt about SIR model

Dear graph-tool community,

I have a little doubt off the topic.
I've been checking out the SIR model. In the mathematical expression
what is the meaning of the variable ri? Was it the likelihood of
spontaneous infection of the node? I checked the references, but I
still couldn't understand.
Can you help me?

Best regards,

Ronaldo Alves

It's right there in the documentation:

      r : ``float`` (optional, default: ``0.``)
         Spontaneous infection probability.


Thank you Thiago,

As the math expression it has the index "i" in the variable "r" and in
the documentation of the parameter a float is expected, not an array,
I figured it could be something else.