Matthew & List, Now this is getting interesting, but it is getting into realms of linear programming about which I am ignorant. But, what the heck: Consider some of the variables: Passengers in city i who want to go to city j (do you accomodate all by point to point service, or by huge -- ugh! -- hubs or by a mixture of point to point and smaller hubs?). And by the way, I do not want to have to show up at the airport before 9 am (others may have getting to the airport at 5 am as an ascetical practice, and God love them for it, but I believe 5 am is a time for sleeping) What aircraft you have in each city & what type; what will be coming in & going out? Where are the crews? What planes are the pilots certified on? Do you have your computers crank out this information at midnight and call folks at 1 am? Or, do you rely on historical data, and get what we have now? But it is an interesting problem. I'd be curious to see someone run it with somewhat realistic data. john On Mon, 19 May 2003, Matthew Montano wrote: > I've been building models that handle scenario's that take nearly 25 > seconds for Excel to recompute,. Now-a-days, the traveling salesman > problem, even over 100k pax a day, is a breeze for modern systems. I > used a Blaze Business Rules Engine that was essentially built for it.. > > ..but I never tried it. > > In the example of making a connection, it becomes a constraint. The > customer has to be in JFK by "X" time. Virtually everything in the > model is a constraint, and you'd simply look for the lowest cost > solution. > > Right now, airlines are still running with 60's models where the > constraints of staff and crew (and scheduling) are such that they > essentially drive the modern airline schedule. Then the revenue > management guys go price the routes to try and fill the planes. > > After the plane flies, the airline then counts it's pennies and > determines if it made money. More often than not ever since about 1970, > they haven't. > > I was just thinking there had to be a better way. > > (Back to my day job.) > > Matthew -- John F. Kurtzke, C.S.C. Department of Mathematics 278 Buckley Center University of Portland Portland, OR 97203 503-943-7377 kurtzke@xxxxxx