Every edge of a Reaction Admissibility Graph belongs to exactly one of ten abstract classes. The classes are the members of the enumeration EdgeClass in edge_classes.py.

#	Edge class	Action
1	GROWTH	same-polarity monomer absorption, \(n \to n+1\)
2	SHRINKAGE	opposite-polarity monomer impingement, \(n \to n-1\)
3	DISSOCIATION	thermal monomer emission, \(n \to n-1\)
4	RECOMBINATION	cross-polarity monomer annihilation
5	ANNIHILATION	cross-polarity binary (cluster-cluster) hyperedge
6	INTER_POPULATION	\(p \to p'\) at fixed size and composition, for example loop-character conversion
7	SOLUTE_TRAPPING	trapping and detrapping, \(c \to c \pm e_s\)
8	COALESCENCE	same-polarity binary growth
9	SOURCE	cascade injection, with no precursor vertex
10	SINK	absorption at a fixed sink

Stoichiometric contract

Each class carries a fixed stoichiometric contract, which is stored as an EdgeClassSpec in the table EDGE_CLASS_SPEC. The contract states:

the number of precursor cluster vertices
the kinetic order of the reaction flux
whether the reaction consumes a same-polarity monomer from its pool
whether the edge crosses the two polarity layers
how the edge shifts the size, the population and the composition
whether the edge creates a vertex (SOURCE) or removes content to a fixed sink (SINK)

The function spec_of() returns the contract of a class.

Because the sign pattern of \(S_{ar}\) is structural, conservation of the signed defect content \(q = \chi n\) holds by construction for every intra-host reaction. It is not derived again for each material.

See also: Reaction Admissibility Graph, Graph walker