Over the past few months, I’ve heard a lot of folks talk about how many ways the ten Callisto projects can be combined. In all cases, the concensus seems to be that there are 10! (ten factorial) combinations. Or at least about that many. That’s 3,628,800 combinations. Wow! Except that it’s actually nowhere near correct.
To start with, the platform (Eclipse) project is required in all combinations. That leaves at most 9! = 362,880 combinations. That’s better. Far more manageable. Of course, when you consider that TPTP needs to have BIRT and that WTP requires EMF, then the actual number of possible combinations is actually quite a lot smaller.
Of course, this isn’t even close to correct anyway…
It’s just not a “factorial” type of combination. Assuming that you need to have the platform in all combinations, you can then either (a) have or (b) not have each of the remaining projects in your combination. Essentially, it’s a binary condition for each of the remaining nine projects. Either WTP is included, or it’s not. Either GMF is included or it’s not. And so on. Basically, you double your possible combinations with the consideration of each additional project.
Again, since platform must be included, there are really only nine projects to consider. So, there are 29 = 512 combinations. Of course, the actual number of combinations is smaller than this since some of the projects are dependent on other projects.
So there you have it. All that university math I took was worth something. At least to me…
