Dear all, I'm using GP for combining 'matrix objects' (for example, matrix A, B and C). I also have a node representing a number (extending ERC class). Then, I would like to evolve individuals such as 'A*B', '2*A + B', 'C*A + 2*B', etc, i.e., my 'complete individual' must return a matrix. I can not, for example, have an individual like '2 + 2' or '3 * 2', because it would return a number (not a matrix). If I use a GE (Grammatical Evolution) I can easily avoid it by using the grammar. How can I avoid it by using GP in ECJ? Is there any way to ensure that I will always have at least one matrix as a terminal node? Best, Márcio -------- Prof. Dr. Márcio Porto Basgalupp Instituto de Ciência e Tecnologia (ICT) Universidade Federal de São Paulo (UNIFESP) Tel: +55 12 3309-9500 (r: 9762)