When producing items, BP2 made random decisions as to candidate rules in the grammar and the position of each derivation. These decisions may also be controlled in "step computation" (see §12).

Sequences of random numbers are predetermined in computers. This means that each time you run BP2 you get the same sequence. If you run an improvisation immediately after starting BP2 you get the same "random" performance... Of course, if the "Autorandomize" button is checked on the upper "Settings" dialog, every piece is likely to differ from tyhe preceding one, but this may not still not be the way you expect a machine to "improvise"!

There are two ways of avoiding this. First, you may want to instruct BP2 to produce anything you've never heard before. For this the random-sequence generator should be reseeded with an arbitrary number, for instance a number computed from the date/time information available inside the computer. Select "Randomize" in the "Misc" menu. You get the little "Randomize" dialog as shown Fig.23. The current random seed number is always 1 when you start BP2, therefore default random sequences are identical. The random seed is saved in the "-se" setting file automatically loaded with each project.

Clicking "Reset" will restart the random generator with the current seed number, thus producing again the same sequence of random numbers. Clicking "New seed" will take an arbitrary number as a new seed and recalculate the sequence accordingly. Now you get something really unpredictable.

Another way of playing with randomness is to type a seed and click "Reset". In this way you select manually one among more than 65,000 sequences (because the seed may be any number between 0 and 65535). If you get a remarkable result with a given value of the seed number, you should note it down carefully or save it along with the current settings (see the "File" menu).

There is no certitude that every future version of Macintosh® will produce the same random sequence starting from a given seed number. In addition, you must keep in mind that if you make changes in the grammar (modifying or moving rules) the sequence is likely to change. If you need more control on productions, either modify the grammar (see for instance "Programmed grammars", §11 infra, or control procedures, reference manual §8.1) or make decisions by hand as shown §12 infra.