9 r( O8 X* D& D. H) p8 z! ]! The Vehicle Routing Problem (VRP); * A% N7 X0 m& n2 @, V. X ' @7 V) G9 V ^8 R. u!************************************; $ y4 I, |! v4 k* B# E* N) a: g" X! WARNING: Runtimes for this model ;. L# M- G" \2 H
! increase dramatically as the number; # B S0 @; } l8 V! of cities increase. Formulations ; ' |6 n; P% b! Z( e$ D; L- z! with more than a dozen cities ;# x$ j8 ~7 y+ P K
! WILL NOT SOLVE in a reasonable ; 5 b0 V# p0 h# K, C8 {2 }- b! amount of time! ; o3 ?) p* @' ?( k* l
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1 b5 o6 m" t" f- l SETS: 5 r2 @/ T- `$ B+ H8 E* C ! Q(I) is the amount required at city I, ! ?! `" n: h* w8 M2 ` U(I) is the accumulated delivers at city I ;$ ]5 W2 E& ]+ L: ]
CITY/1..8/: Q, U;; s; B* P6 g& i* D$ f% R3 j2 P
5 R: C' F1 h- X( O2 G' X2 z8 P! P ! DIST(I,J) is the distance from city I to city J % B9 O3 C" `% s. k' f1 m X(I,J) is 0-1 variable: It is 1 if some vehicle9 s \( r* z/ |. ] v. g9 A. J* |
travels from city I to J, 0 if none; 1 D9 I7 J3 [9 U3 i7 ` ^( n" g CXC( CITY, CITY): DIST, X; ! c: E$ L# W5 G4 ] ENDSETS( k5 M4 U4 ]5 _1 y2 B
! |8 V" [4 [6 K% C0 t# a: T! \ DATA:8 m# c# V0 \* n, Z* d: J
! city 1 represent the common depo;7 I& D9 ?$ i1 W
Q = 0 6 3 7 7 18 4 5; ; |6 }6 H. P, H! Y3 x* c : g% T: L" f' d4 @/ m7 g ! distance from city I to city J is same from city ]8 S; I: q! T1 F) q4 l: C J to city I distance from city I to the depot is $ S/ Y4 m! M# w3 g: q& o 0, since the vehicle has to return to the depot;; c* k7 [; [9 S' m: Y
. k1 S, l7 O v% L6 x0 [$ ~ DIST = ! To City;& p% B. a3 O+ d5 M! r ~5 n
! Chi Den Frsn Hous KC LA Oakl Anah From; ; h8 T! c, U$ v- Z3 A8 M; U7 Z 0 996 2162 1067 499 2054 2134 2050!Chicago; / Y! c7 {) h9 z4 z/ K 0 0 1167 1019 596 1059 1227 1055!Denver; : a+ U& x3 I2 m- M7 F7 O) n& s' i 0 1167 0 1747 1723 214 168 250!Fresno; 1 J+ ~) m$ w8 }# m( ^" _1 d 0 1019 1747 0 710 1538 1904 1528!Houston; / d- p0 x$ {& Z9 K 0 596 1723 710 0 1589 1827 1579!K. City; ( |9 W% Z8 l7 b* d. f 0 1059 214 1538 1589 0 371 36!L. A.; 9 J) _6 T& `3 }) Z* T" ?& j 0 1227 168 1904 1827 371 0 407!Oakland; ! U" q, ?6 G' t2 |* k 0 1055 250 1528 1579 36 407 0;!Anaheim;2 Z4 p6 {! R X
) }! k% M9 m, ]: Y; R1 { ! VCAP is the capacity of a vehicle ; 1 `8 l" w2 M3 ~! R1 m( W VCAP = 18; ! U% c/ i6 }3 [! g. t5 W ENDDATA o8 b* @$ H% |" M6 P
* h7 O) W( W9 c, ]& k) o ! Minimize total travel distance; ( ~8 k/ \$ @( U( [% M MIN = @SUM( CXC: DIST * X); 6 r1 ^: h; l+ Y: W" _) d 7 Q, }) w; D0 H9 a- f3 U ! For each city, except depot....; ( K7 D$ A" r8 F2 I u7 y$ M* ^0 s @FOR( CITY( K)| K #GT# 1: 8 d: o1 N z+ j C7 G y" V6 `$ [) |" `9 b
! a vehicle does not travel inside itself,...; / k2 k7 V- j* C- o! p X( K, K) = 0; e$ ^+ C+ b+ o
: H( \7 k- ]1 C" W% F% q& u
! a vehicle must enter it,... ;% @, A5 A( S4 @
@SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR# 8 n; Q, [; i/ @ [* X- ? Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;- E. H- D% q% v+ c" |% V
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! a vehicle must leave it after service ; 1 C" G0 h, V% M6 c @SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR# G3 V# p, A! D8 u9 k! k% R
Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;+ j0 J9 u0 \% n! a1 }8 `
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! U( K) is at least amount needed at K but can't % p: {7 A8 q7 \1 n8 h exceed capacity;+ }: E, ~+ f& ^7 d" p
@BND( Q( K), U( K), VCAP);* a' C! b2 c0 l2 F
# H3 |: w1 D2 s( K" W1 M' t0 e
! If K follows I, then can bound U( K) - U( I); & z3 q- m1 G5 L1 W @FOR( CITY( I)| I #NE# K #AND# I #NE# 1: 2 Q; t# d5 U% u* h
U( K) >= U( I) + Q( K) - VCAP + VCAP * * h9 P( O. a; T$ A- P! t
( X( K, I) + X( I, K)) - ( Q( K) + Q( I)) ) I! ]! ~2 R5 x * X( K, I); & c$ R8 \3 a! f% I% c2 X: Z ); 6 N$ V% X! R: v% \, t. t& w* z A7 A6 ?6 I% T
! If K is 1st stop, then U( K) = Q( K);; Z8 i @& r4 ^5 z
U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);4 D& o8 R5 D, w: Z5 O
! b& U" R; ~1 o! ~% W D. h" R& g6 Z+ Y ! If K is not 1st stop...; & `0 I5 s: E2 Z5 w U( K)>= Q( K)+ @SUM( CITY( I)| # g. z- C$ i: _2 i
I #GT# 1: Q( I) * X( I, K)); / W `) c1 ~% _5 S6 X! j+ ?8 R );9 I3 E4 }$ n m* O4 X& }