The normal of the surface will initially be pointing in the z-direction, so it might be a good idea to change the settings in Maya so that its z-axis points upward. Do this from the menu Window->Setting/Preferences->Preferences in the lefthand menu, choose Settings and there you will be able to change axis. Also it might be easier to view what is happening without the grid, turn it off on the Display-menu.
Attractors act like magnets for the surface. As it grows it draws closer to the attractor. Attractors and repellors are represented as point charges and have to parameters, a constant and an exponent. The displacement from an attractor is diplacement = c/d^e, where d is the distance to the surface element, c is the constant and e is the exponent. This function has a singularity in d=0 and thus you get strange (and perhaps undesired) results if a surface element is close to the attractor.
Attractors are created in a separate layer, this makes it easy to toggle their visibility.
Repellors are similar to attractors, instead of drawing the surface closer, it is pushed away.
Gravity is a force that acts uniformly throughout space in one direction (x, y, or z). You can set the gravity with the -g/gravity flag.
You can set boundaries for the growth by placing ordinary Maya-surfaces (polygons or nurbs) in the scene. Before starting genr8, you need to place the surfaces on the selection-list before running the command. There are three different wall behaviours defined, that you can choose between before the run.
The growth is cut off so that the surface do not penetrate the boundary. During testing there have been cases where the, boundary does not stop the growth. The reason for this is most likely because Maya failed to detect the intersection
As the surface element hit the boundary, all movement is stopped. With the default behaviour, it slides along the boundary, but now it stops dead instead.
This behaviour is only interesting when you have evolution. The surface can grow past the boundaries, but their fitness is penalized as they do so.
The seed (starting surface) for GENR8 is by default a regular polygon. The user can control the length of the sides and the starting position of this polygon. However, GENR8 can also handle user defined seeds. You can draw a curve and select it before starting the run (you do not have to close the curve, GENR8 will do that for you). This curve will be tha starting point for the run, predicting the result is difficult though, since the assignment of types for the segments is randomized.
Since GENR8 uses Bsplines rather than nurbs, it is recommended that you use the "Curve with EPs" rather than the "Curve with CVs" tool. Otherwise, the output from GENR8 will have a different shape from the input. GENR8 assumes that the normal of your axiom has some component in the z-axis, if not things might go wrong.