144 lines
7.8 KiB
Plaintext
144 lines
7.8 KiB
Plaintext
Welcome to Gem-graph !
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Gem-graph lets you move and transform drawn objects using an automaton. It's an
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ideal tool for describing the evolution of a situation through drawing. Would
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you like to see your drawings evolve automatically to represent a phenomenon?
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Gem-graph lets you transform your drawings as you wish. You can draw whatever
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you want. It's your drawing and you decide how it evolves! You can use gem-graph
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to make a game. You can use it to make a model of a phenomenon that interests you.
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You can represent what you want simply or in more realistic detail.
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Simple parts and more detailed parts can coexist in the same design. You can
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watch what you have created evolve without interfering or guiding it towards what
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you want to achieve. You can mix several drawings and animations. You can observe
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them in detail, modify them, go back, start again, measure, compare and keep the
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results that interest you so that you can play them again.
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However, a certain amount of effort will be required to achieve this. A complicated
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model will require more work than a simpler one, but it is possible to start with
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something simple and develop it step by step. In any case, you must draw what you
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want to see and say how you want it to be transformed. Gem-graph cannot do that
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for you. Gem-graph can only help you to draw up and develop your idea. However,
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it can give you powerful tools to do so. The strength of gem-graph - short for
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'geometric graph' - lies in the fact that it deals only with very simple drawing
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elements, all of which are similar, and that the rules it uses to manipulate these
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elements are equally simple and similar. As a result, these rules can be combined
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and processed automatically, no matter how many there are. The tools provided by
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gem-graph give you access to the power of the automaton it uses to draw and animate
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your drawings, and this manual is here to help you to learn how to master them.
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One way of doing this is to reproduce a very simple example, such as when a word
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processing program asks you to write "Hello world". For gem-graph, the equivalent
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of "Hello world" will be to move a small line on your screen. Once you have done
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this simple example, you will know enough to quickly build and animate much more
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complex drawings that suit your desires. If you like learning this way, this
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example is explained (here). If you prefer to learn by reading what the commands
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you see on the screen are doing, they have been detailed (here). The table of
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contents goes from the simplest to the most complicated. How to set up a simple
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model, observe it and measure what it does, then transform it by changing what
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you see and how it reacts.
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------------
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Our "Hello world" is the simplest program that gem-graph can execute. It consists
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of a single short arrow, which moves in a straight line in a single direction.
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To do this, we first had to draw this little arrow and then make it move. The
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result is certainly not very exciting, but this example is enough to show how a
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drawing is made and how it is animated. One state and one rule are enough. The
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rule only says: if an arrow is drawn here, I erase it and redraw it on the next
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square. For the moment, you don't need to know in detail how the rule works
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(it's described here). All that gem-graph needs to know is written in the
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"Hello world" file (here). If you open this file, you'll find a description of
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the arrow (here) and its movement (there).
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To improve this model, it is possible to give the arrow the ability to move in
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two directions: forwards or backwards. To do this, we need to add a second rule.
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This second rule says: if an arrow is drawn here, I erase it and redraw it on the
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previous square. A random draw (described here) is also necessary to determine
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whether the first or second rule applies. With these two rules and the random
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draw, the arrow now sometimes goes forwards, sometimes backwards. We can call
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this second model a "random walk".
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The second model (the random walk) had one state (the arrow) and two rules
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(forward/backward). Now here's a model with two states and two rules:
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the pendulum. This time, the arrow can be drawn either tilted forwards or tilted
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backwards (these are the two possible states) and the two rules switch the drawn
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arrow from one state to the other or vice versa. In the file, the states are (here)
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and the rules (here). The pendulum does not change place, but alternates between
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left and right. Like the previous ones, you can slow down the programme so that
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you can observe the movements.
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Once you know how to write a state and a rule, you can write thousands of them:
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they will always be combinations of the same elementary form. However, it is also
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possible to combine programs: for example, you can combine the reports and rules
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from the two previous models to create a new model that shows both phenomena
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simultaneously. Once again, in the file, the states are (here) and the rules
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(here).
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The next example shows how the same rule can be applied to a multitude of states.
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The rule is the same as that used in the first model: an arrow can only be moved
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one square forward, but this time you have to check that the square forward is
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free. If it isn't, the arrow won't move. Once the rule has been modified in this
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way, it can be applied to a multitude of arrows distributed randomly in space
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(see details here).
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When you set the model in motion, you will see all these small lines moving from
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left to right. A single rule is responsible for all these movements.
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For a small fee, we can apply the two rules of the 'random walk' model to all the
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arrows distributed in this space, and they will then all behave in the same way,
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sometimes moving forwards, sometimes backwards.
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In the next example, we first build a model similar to the previous one: a
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multitude of arrows are randomly distributed in space, but this time they are
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vertical and the movements are up and down instead of right and left. Then, we
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add this model to the previous state and set the final model in motion. We see
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then little lines moving from left to right or reverse if they are horizontal,
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and up and down or reverse if they are vertical. Their number is constant. They
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don't change shape or direction. There seems to be no accident when they cross.
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Nothing else happens.
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The last example in this series, because it shows a multitude of diverse and
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simultaneous movements, perhaps gives the impression of a more complex system.
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It would be easy to make it even more complex, but it's much more interesting
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to show how gem-graph can be used to analyse and control that complexity (here). At
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this point, it's time to compare gem-graph to other classes of automata that do
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quite similar things, and to look at what it can actually do and what its
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limitations are.
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The main difference between gem-graph models and agent-based models is that
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gem-graph deals with situations, not agents. In a situation where several agents
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are interacting and each agent could apply a different rule, gem-graph considers
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and processes the situation. Not the agents. Whatever the state - the new
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situation - that results from his action, his decision-making process will have
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been simple and straightforward. It will therefore be easy to modify and control.
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And the diversity of possible new situations will be far greater than that
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offered by agent-based models.
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The comparison between gem-graphs and cellular automata first comes up against
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a question of vocabulary. What is commonly called a 'rule' in one and the other
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is not the same thing. Gem-graphs and cellular automata have the same power:
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anything that can be done by one can be done by the other, but their writing is
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not the same (details of this comparison here).
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How can gem-graph be used to analyse and control the complexity of what it
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represents and sets in motion? This chapter introduces the gem-graph mechanism.
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