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+# GE-ometric D-irected M-ulti-GRAPH (gem-graph)
+
+### (1) A geometric graph is a graph whose nodes have coordinates in a space
+### (2) It is directed if its links are arrows
+### (3) It is a multigraph if several arrows can be superimposed from one node to another
+
+##### NB "directed" does not mean "oriented": a graph is oriented if one of its nodes is its root.
+
+#### Directed geometric multigraphs have properties that make them suitable for the representation of complex phenomena. gem-graph is a software that allows modeling by rewriting a directed geometric multigraph.
+
+---
+
+### Project documentation:
+* questions about the [architecture](architecture.md): identification and naming of the main parts of this program and the data structures.
+* questions about the [theory](theory.md): properties of rewritten geometric directed multigraphs. (JS. Dec 2017)
+
+---
+
+Faced with the difficulty of computing the evolution of complex systems defined by
+   a great diversity of objects and
+   a large diversity of interactions,
+
+The rationale for the gem graph is:
+
+1. To represent the space
+2. A discrete space (not continuous)
+3. A uniform and Cartesian space
+4. Links can be established between some of these units
+   They allow to draw objects (isolated related parts of the graph) and situations (relative positions of objects)
+   for practical reasons, it is convenient to use arrows and to allow a large number of them to be stacked from one node to another
+5. An automaton, i.e. a set of states and transitions can rewrite this space, with version management
+6. The states can represent the space
+   Here, the space can be understood as a representation or an approximation of a real space.
+   But a state can be a space as well as a set of symbols (e.g. tags)
+   which can be drawn in the graph using the same encoding or it can be any combination of the two.
+7. Transitions are all combinations of a single elementary transition type consisting of:
+   - a single condition (how many arrows at this point? - compare to a predefined number))
+   - a single assignment (define n arrows at the same place)
+8. The coding of static information (states) and dynamic information (transitions) is distinct.
+   The purpose of this restriction is to maintain a strict homogeneity of the rules (cf. §7)
+   which is the condition for their automatic management and editing.
+9. Constraint on granularity: the range of arrows between spatial units is increased by the local space (discrete/continuous ?)
+10. The calculation is local, random (choice of orientation of the local space, choice of the result of the actions of two rules whose set of conditions is superimposable), asynchronous
+11. Interfaces are possible with statistical and/or continuous fermion models.
+    Time and space are then superimposed and the conditions to intensive local variables 
+    (concentrations, temperatures, flows, etc ...) can be accessed by means of a specific gem-graph condition
+12. Interfaces are possible with boson representations.
+    Time and space are then superimposed and conditions on local intensive variables (flux, cross section, etc.)
+13. The topology, dimension and magnitude of the space are not constrained
+14. Represent and optimize graphs
+
+
+---
+> Locos, formas modumque cohérentiae omium rerum status depingit. Nihil Aliud comprend.
+> Eas res praecepta movet aut transformat. Nihil aliud facit. Quaedam transforme en sua potestate sunt.
+> Aliae transforme alii succedere debent.
+> Interpositus status inter illas et istas jacet.
+> Ab antecedente statu primarum ad sequentem statum secundarum iter nullius est nisi per suorum interpositum statum.
+---