$title Aircraft Allocation under uncertain Demand (AIRCRAF,SEQ=8) $onText The objective of this model is to allocate aircrafts to routes to maximize the expected profit when traffic demand is uncertain. Two different formulations are used, the delta and the lambda formulation. Dantzig, G B, Chapter 28. In Linear Programming and Extensions. Princeton University Press, Princeton, New Jersey, 1963. Keywords: linear programming, aircraft managing, allocation problem $offText Set i 'aircraft types and unassigned passengers' / a*d / j 'assigned and unassigned routes' / route-1*route-5 / h 'demand states' / 1*5 /; Alias (h,hp); Table dd(j,h) 'demand distribution on route j' 1 2 3 4 5 route-1 200 220 250 270 300 route-2 50 150 route-3 140 160 180 200 220 route-4 10 50 80 100 340 route-5 580 600 620 ; Table lambda(j,h) 'probability of demand state h on route j' 1 2 3 4 5 route-1 .2 .05 .35 .2 .2 route-2 .3 .7 route-3 .1 .2 .4 .2 .1 route-4 .2 .2 .3 .2 .1 route-5 .1 .8 .1 ; Table c(i,j) 'costs per aircraft (1000s)' route-1 route-2 route-3 route-4 route-5 a 18 21 18 16 10 b 15 16 14 9 c 10 9 6 d 17 16 17 15 10; Table p(i,j) 'passenger capacity of aircraft i on route j' route-1 route-2 route-3 route-4 route-5 a 16 15 28 23 81 b 10 14 15 57 c 5 7 29 d 9 11 22 17 55; Parameter aa(i) 'aircraft availability' / a 10, b 19, c 25, d 15 / k(j) 'revenue lost (1000 per 100 bumped)' / (route-1,route-2) 13 (route-3,route-4) 7 route-5 1 / ed(j) 'expected demand' gamma(j,h) 'probability of exceeding demand increment h on route j' deltb(j,h) 'incremental passenger load in demand states'; ed(j) = sum(h, lambda(j,h)*dd(j,h)); gamma(j,h) = sum(hp$(ord(hp) >= ord(h)), lambda(j,hp)); deltb(j,h) = (dd(j,h) - dd(j,h-1))$dd(j,h); display ed, gamma, deltb; Positive Variable x(i,j) 'number of aircraft type i assigned to route j' y(j,h) 'passengers actually carried' b(j,h) 'passengers bumped' oc 'operating cost' bc 'bumping cost'; Free Variable phi 'total expected costs'; Equation ab(i) 'aircraft balance' db(j) 'demand balance' yd(j,h) 'definition of boarded passengers' bd(j,h) 'definition of bumped passengers' ocd 'operating cost definition' bcd1 'bumping cost definition: version 1' bcd2 'bumping cost definition: version 2' obj 'objective function'; ab(i).. sum(j, x(i,j)) =l= aa(i); db(j).. sum(i, p(i,j)*x(i,j)) =g= sum(h$deltb(j,h), y(j,h)); yd(j,h).. y(j,h) =l= sum(i, p(i,j)*x(i,j)); bd(j,h).. b(j,h) =e= dd(j,h) - y(j,h); ocd.. oc =e= sum((i,j), c(i,j)*x(i,j)); bcd1.. bc =e= sum(j, k(j)*(ed(j)-sum(h, gamma(j,h)*y(j,h)))); bcd2.. bc =e= sum((j,h), k(j)*lambda(j,h)*b(j,h)); obj.. phi =e= oc + bc; Model alloc1 'aircraft allocation version 1' / ab, db, ocd, bcd1, obj / alloc2 'aircraft allocation version 2' / ab, yd, bd, ocd, bcd2, obj /; y.up(j,h) = deltb(j,h); solve alloc1 minimizing phi using lp; display y.l; y.up(j,h) = +inf; solve alloc2 minimizing phi using lp; display y.l;