General algorithm for divisional leagues

[Bitruder]

I need to setup a schedule for a league with 10 teams, split into two divisions of 5 teams each.
Each division will basically be it's own round-robin tournament (but you play 4 games against each team - twice home and twice away).  However, I also need each each team to play two games against each team in the opposite division (one home one away).

I believe this works out to a total of 26 games for each team (4*4=16 inter-divisional and 5*2=10 for extra-divisional).

I'm not sure how to schedule the games for extra-divisional play.  For inter-divisional I can use one of the tables from this site I believe?  The games are spread out over a couple of months, so I figure I'll just take one of those tables and slot them into the available game times (so slot 1 might be over 2 weeks for example).

I hope I'm clear on what I'm trying to accomplish.  I'm interested in a final solution, but more so on the technique for doing it so that I could hopefully do it myself in the future!

Thanks

[Ian Wakeling]

The following outlines one possible path to a solution (untested!).

Download my Excel round-robin generator and use the "Home-Away" feature to generate schedules for 5 teams.  Within each division take one schedule, and add its complement where all home matches have been swapped with away matches, and vice-versa. Repeat this with another randomization of the basic schedule to give 4 games against everyone else within a division in 20 rounds.  Now it should be possible to rearrange the order of the rounds within each division such that the pairs of byes from the 20 rounds correspond to 20 out of the 25 different pairings of teams from the two different divisions.  Note you have to be careful that the 5 remaining extra-divisional pairings can all be played in a single round.  Finally you need to add in 5 more rounds of extra-divisional play, for which you could use the following schedule.

(A1 B1) (A2 B2) (A3 B3) (A4 B4) (A5 B5)
(A2 B3) (A3 B4) (A4 B5) (A5 B1) (A1 B2)
(A3 B5) (A4 B1) (A5 B2) (A1 B3) (A2 B4)
(A4 B2) (A5 B3) (A1 B4) (A2 B5) (A3 B1)
(A5 B4) (A1 B5) (A2 B1) (A3 B2) (A4 B3)

Above if every A division team plays at home and every B division team plays away then you assign the opposite venues for the same pairings in first 21 rounds.  You may want to mix the home/away assignments up a bit, but the same principle applies, whatever venues you assign to the table above, just assign the opposite to the other pairing.