The "Ideal Distance" and "Y-ideal Distance" fields rule distances between nodes. In the tree-parts of the graph, "Ideal Distance" and "Y-ideal Distance" are respectively the horizontal and vertical distances between nodes. In the "loop-parts" of the graph, the energy algorithm tries to ensure a uniform distance equal to "Ideal Distance" between two linked nodes.
The field "Max Nb of Steps" allows you to set the maximum number of steps for the energy algorithm. One step corresponds to the modification of the position of one node. When setting the maximal number of steps you should remember that each node needs to be placed, and its position optimized, and that this is all the more costly that the structure of the loop is complex (high number of nodes / edges). If the number of steps specified is less than the number of nodes to place, the "Fast" option will be used instead.
The Fast option disables the use of the energy algorithm for drawing the loops when ticked. The nodes belonging to a loop are then uniformly placed on a circle, in an attempt to form a regular polygon. This option significantly speeds-up the algorithm. There are several cases in which you may want to choose this option :
if you know that the loops in your graph are indeed forming regular polygons ;
if you know that the loops in your graph are "small" (then this is likely to yield satisfactory results) ;
if you want to draw a large graph, and do not care for an optimal drawing of each loop.
The "Start Again" option allows you to restart the drawing algorithm from scratch without having to reset your model.