<img src=“https://travis-ci.org/cclausen/petri_net.png” />

<img src=“https://codeclimate.com/github/cclausen/petri_net.png” />

I implemented most of the basics you need for playing with PetriNets but there are a lot things to add. Next big step will be a stochastic analysis of the PetriNet.

This package provides a ruby based simulation package for Petri nets. You can build PetriNets, fire transitions and calculate statistica or solve problems in the net. It also provides a visualization of the net (and even the Reachability Graph of the given net)

• en.wikipedia.org/wiki/Petri_net - Wikipedia

At first you need to create a blank petrinet:

net = PetriNet::Net.new

Then you can add places and transitions:

net << PetriNet::Place.new
net << PetriNet::Transition.new

It’s a good idea to name the places and transitions, as you need to refer to them to add, so the better way will be:

net << PetriNet::Place.new(name: "A")
net << PetriNet::Transition.new(name: "a")
net << PetriNet::Arc.new(source: "A", destination: "a")

As you see, an arc needs to get a source and a destination. You can, but you don’t need to name your arcs, as you don’t need to refer to them later in most cases. You can get a place/transition/arc by

net.get_place( name )
net.get_transition( name )
net.get_arc( name )

Or if you know the id (but not the name) you can use

net.get_object(id)

Of course you can save the Objects while creating them and add them afterwards:

place_B = PetriNet::Place.new(name: "B")
net << place_B

or

net.add_object place_B

or

net.add_place place_B

if you want to use this. PetriNet#add_object even accepts arrays of accepted objects

To create an arc you do not need to specify source and destination, you can add them with “add_source” and “add_destination” later on, but an arc has to have both before being added to a net.

!!! Attention, I'm not sure how I will implement markings in the end, this part might be wrong because I changed something. I'm not happy with the way I handle markings/token currently. Currently are PetriNet::Base-Objects which makes no sence in my opinion.

!!! Attention, Markings are inconsistens at the moment. In the original code markings are what I call "token" or "tokken" and a marking is the "state" of a petrinet, which means how many token are in which places. It's hard to understand which markings are meant as currently everything is called "marking" I will refactor this some time.

You can create markings like other PetriNet::Base objects with

marking = PetriNet::Marking.new

And add them to a place with

place_B.add_marking(marking)

But since I see no sence in creating the specific markings you can do

place_B.add_marking(3)

to add three markings to a place. Without any argument it will add just one marking.

You can get the current marking with net.get_markings. This will give you an Array of state-markings. [1,3,2,4] would mean, the first place (in order of id’s, but be careful, every PetriNet::Base-object has a unique id) will hold one marking (or token) the second place will hold 3 and so on. You can even set the markings with

net.set_markings([1,3,2,4]

but be carefull with this one, maybe this should be private in future but it can be very usefull to save the initial state or to set the net to a specific state for some algorithms (e.g. for generating the Reachability Graph)

You can just print yout PetriNet with

net.to_s

as you should know this means you can write

puts net

For a more fancy way to show off with your PetriNet you should try

net.to_gv

which generates the GraphViz-Code for the PetriNet. It is planned to use the GraphViz-gem in the future to create png and stuff like that directly.

The Reachablility Graph is a Graph with nodes representing reachable markings of the net in the current state and edges reresenting the transitions you need to get from one node to another. You can generate the reachablility Graph with

net.generate_reachability_graph

As a PetriNet itself you can to_s and to_gv the reachablility Graph too.

Neither the library nor the documentation is finished by now, so please feel free to contribute

Just write an email and/or fork this project. Active contributors will get write-access to this repository too.

This library is available on rubygems.org soon