Formalising Design Exploration as Co-Evolution

This paper introduces a model for design exploration based on notions of evolution and demonstrates computational co-evolution using a modified genetic algorithm (GA). Evolution is extended to consider co-evolution where two systems evolve in response to each other. Co-evolution in design exploration supports the change, over time, of the design solution and the design requirements. The basic GA, which does not support our exploration model, evaluates individuals from a population of design solutions with an unchanged fitness function. This approach to evaluation implements search with a prefixed goal. Modifications to the basic GA are required to support exploration. Two approaches to implement a co-evolving GA are: a combined gene approach and a separate spaces approach. The combined gene approach includes the representation of the requirements and the solution within the genotype. The separate spaces approach models the requirements and the solutions as separately evolving interacting populations of genotypes. The combined gene approach is developed further in this paper and used to demonstrate design exploration in the domain of braced frame design for buildings. The issues related to the coding of the genotype, mapping to a phenotype, and evaluation of the phenotype are addressed. Preliminary results of co-evolution are presented that show how exploration differs from search.