HalfBuilder simply calls GrowBuilder or FullBuilder with a certain probability. So the only possible difference would be in your parameter settings. And so it is: >> gp.koza.half.min-depth = 12 >> gp.koza.half.max-depth = 55 >> >> gp.koza.grow.min-depth = 5 >> gp.koza.grow.max-depth = 13 55 is a HUGE number, which will generate gigantic trees. Consider if HalfBuilder tries to make a full tree of depth 55 and your trees average to binary. That's O(2^55) nodes. Ordinarily these methods have min and max values set somewhere between 2 and 7. Traditionally grow is set to 5 and 5 (for mutation), and half is set to 2 and 6 (for initialization). I wouldn't deviate from that much. Sean On Apr 10, 2011, at 9:21 AM, Pawan Kumar wrote: > same code works fine if I use GrowBuilder, FullBuilder but create > problem with HalfBuilder.