Gene Definition

The simplest construct of the DARWIN language is the gene. The genes are used to build up chromosomes. The DARWIN gene implements the initializer, printer, crossover, mutator and evaluator as its moderators.

The gene definition syntax is as follows :

gene_typedef	::=	"gene" id
		"{" memb_decls "}"
		genome_moderators ";"
genome_moderator	::=	initializer ":" prototype
	$\vert$	crossover ":" prototype
	$\vert$	mutator ":" prototype
	$\vert$	evaluator ":" prototype
	$\vert$	printer ":" prototype

For example, a gene representing a rectangular region is defined as follows.

gene TRectangle
{
  char x;
  char y;
  int orientation;
  frozen int width;
  frozen int height;
}

Note the usage of keyword "frozen", which instructs the compiler that no special handling for these members is needed, that is no code effecting these data members will be generated.

In addition, we have not used the full expressive power of the DARWIN gene definition, which allows specifying domain information on a given member. For example, if a rectangle can be positioned only at discrete x and y coordinate values in the range [0..100], then we have the following gene definition :

gene TRectangle
{
  char x < [0..100];
  char y < [0..100];
  int orientation < [0,1];
  frozen int width;
  frozen int height;
} < evaluator : RectangleEval, init : RectangleInit;

Now we have a better representation of our gene, and the evaluator moderator specified. Since the crossover, mutator and printer are not specified, the DARWIN compiler is instructed to generate default handling code for these moderators. Note that the names of the moderators can be abbreviated.

The DARWIN gene definition is a set of basic typed data members, which may optionally specify domains. The semantics of the gene definition is defined below.

The gene initializer

is called when a new gene is created by the DARWIN program. Usually this happens as a result of creating a chromosome, which in turn initializes all its gene members. The initializer if not specified, is generated by the compiler by looking at the gene member domains. The domain of a data member not specifying a more restrictive domain is taken to be the data space of the underlying data type. The generated initializer produces statements to randomize each of the non-frozen gene members, by taking into concern its domain.

The gene crossover

moderator is responsible for providing the crossover operator on the gene. It can be called by the chromosome crossover moderator if a gene member of the chromosome is selected as a crossover point. The default gene crossover operator implements a one-point binary crossover.

The gene mutator

implements the mutation operator. This function creates an anomaly in the gene and is calls by the chromosome mutator if a population decides to mutate a chromosome, which in turn selects to mutate the given gene. The generated gene mutator performs a bit flip at a random position if no domain is specified for the member at the given gene position, and a domain specific randomized change otherwise.

The gene printer

is provided for printing the values of the gene members in a more readable form.

The gene evaluator

is only needed if no evaluator for the chromosome containing the given gene is provided. In such a case, the evaluator should provide a floating-point value specifying the measure this gene contributes to the total welfare of the solution encoded by the owning chromosome. No default evaluator can be generated by the DARWIN compiler.