0 x" _7 s9 l8 z. [: O' w- x! The Vehicle Routing Problem (VRP); 1 ~, O, I( x& B1 u; i6 K/ J; o' w" D
!************************************; ! x) \$ _8 G0 I! j! WARNING: Runtimes for this model ;. h* b V8 A1 n
! increase dramatically as the number; . U' K3 r& { S5 }) s0 o! of cities increase. Formulations ; # v& }! {) \' W6 }! with more than a dozen cities ;: s7 {" Q! c7 K( V7 T
! WILL NOT SOLVE in a reasonable ;8 O+ e$ D$ L7 L" L- c
! amount of time! ; : d# x Q8 \+ j# o+ @$ U!************************************;8 M5 u$ `: c' E D
0 J9 M. l. o. L) \0 o! \6 U5 y' v
SETS:" D! C9 D, s& M* ]8 u
! Q(I) is the amount required at city I,4 r0 `4 j! X6 i& O3 n+ P6 F
U(I) is the accumulated delivers at city I ; $ C) O" l' Z3 t CITY/1..8/: Q, U; ' Z; e5 }" @9 \/ C* j3 F. m( P- h! i& S& U, e% h8 u
! DIST(I,J) is the distance from city I to city J , V q, |; q- |2 k' a& o7 F X(I,J) is 0-1 variable: It is 1 if some vehicle 1 N' D3 r$ T6 r% N' ^# u travels from city I to J, 0 if none; * \5 ]4 k5 I0 i8 t: t CXC( CITY, CITY): DIST, X; 1 Y* i3 I# q ^& N- \ ENDSETS9 x+ N4 m+ ^6 x' z( q
3 I+ a4 D& V) G0 M+ v v+ e5 M
DATA: , a0 E" A' n* G! k& \ ! city 1 represent the common depo; o3 e T+ Y Y5 z: r% N+ |0 S! i Q = 0 6 3 7 7 18 4 5;6 M( y2 A+ k d4 p2 C. G2 y* W& d
9 F- Y0 _9 U6 n! ]7 n; w
! distance from city I to city J is same from city 3 C+ u6 J4 P W0 I- V J to city I distance from city I to the depot is ! i1 r! q" Y/ X. ~, f8 x 0, since the vehicle has to return to the depot; 0 C* a, w4 u% }9 r* x! J7 ?* `* D# j4 U. v" O# h9 K* `
DIST = ! To City; ; }. f7 x* m. y ! Chi Den Frsn Hous KC LA Oakl Anah From; 8 I: y, d. S6 ]. l8 V0 y4 y2 ?7 L9 G 0 996 2162 1067 499 2054 2134 2050!Chicago; * z9 N1 \6 C" H: r) O. p 0 0 1167 1019 596 1059 1227 1055!Denver;" _3 s; @$ t, E8 x9 {8 k
0 1167 0 1747 1723 214 168 250!Fresno; , d7 }. N, t/ g, {9 f 0 1019 1747 0 710 1538 1904 1528!Houston;# J# _3 V2 E+ d4 ^
0 596 1723 710 0 1589 1827 1579!K. City;: x& p3 L: d% r
0 1059 214 1538 1589 0 371 36!L. A.; . Q# y0 W% K" o; b! c" B3 x2 ]; E 0 1227 168 1904 1827 371 0 407!Oakland; : h) V9 z3 H0 h+ j' q7 m7 p! ~ 0 1055 250 1528 1579 36 407 0;!Anaheim; # ^8 x) L+ R5 F! D ' }: I- P, w! ^2 ] ! VCAP is the capacity of a vehicle ;/ ]& W3 X4 x% S0 u
VCAP = 18; 5 C' ~) Q/ _# a ENDDATA& _% H4 I( ~( H0 n6 }) @
0 l% N3 [1 S; c/ W: R1 k: z0 M ! Minimize total travel distance;; L2 l% U. X4 w1 E/ L4 q) B( C
MIN = @SUM( CXC: DIST * X); ) @3 E* T9 I. x3 R' O* l: Q' l# h! S( q+ l) B$ ]
! For each city, except depot....;6 j* d- A7 h( }; z
@FOR( CITY( K)| K #GT# 1: . J- E( W! _% H+ u/ V$ }% p ) Z4 J3 n" Z. x4 }8 e, |7 Y ! a vehicle does not travel inside itself,...;" A5 p( s% F3 d" ~0 q/ |
X( K, K) = 0;( ^( Z3 @% x! |) n
; d5 Z" ^: ]2 T0 X- | ! a vehicle must enter it,... ; ( a1 l( v @6 O; }. s/ w; N! B" ~ @SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#: L% i( ^7 v" A6 h, O9 n9 D# y
Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1; 7 _/ `' _) f2 |; M! Y _ , b+ ~6 Q" s8 V ! a vehicle must leave it after service ; 8 N3 M+ D1 R" }: Z @SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#3 L% Q6 C0 I# Z1 u* J% J
Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1; + a6 m( d$ R* V5 N1 h1 ^% _1 @ d/ j* [# F* r
! U( K) is at least amount needed at K but can't 9 V" p! P( z' x7 o3 N/ ]
exceed capacity; & R: L& |# Y7 a& G( e' q: g @BND( Q( K), U( K), VCAP); , B' X3 W' c2 C" t! @ 3 e# l9 g2 u" S& K* Z, X9 }# ^ ! If K follows I, then can bound U( K) - U( I);; ~$ U( K% b6 c# x3 @' u
@FOR( CITY( I)| I #NE# K #AND# I #NE# 1: ' y, I! {- \; i' S5 \$ ~7 C U( K) >= U( I) + Q( K) - VCAP + VCAP * : P$ ]+ X' |8 [0 u- V
( X( K, I) + X( I, K)) - ( Q( K) + Q( I))' }8 G; S. N0 j! W/ q! ^8 {/ ~
* X( K, I); # z& r* `6 p g5 o+ l% T8 L) p ); # y9 }$ ~2 ?1 ] 3 o: D5 j4 ~1 x ! If K is 1st stop, then U( K) = Q( K);% X3 Z$ t4 H/ y* r/ C; @, g
U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);2 W# P4 q0 p8 e/ S, C# j
8 ~8 i; y/ g6 O" o! G) O9 {3 ? ! If K is not 1st stop...; ( Z0 t( c& j# r$ O( w) n+ O U( K)>= Q( K)+ @SUM( CITY( I)| * ~& c; k/ d E* V
I #GT# 1: Q( I) * X( I, K));2 R, D( ^* i4 ?
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