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! WARNING: Runtimes for this model ;" [2 ?3 \ ~4 c3 z0 |
! increase dramatically as the number; ) Y: e; K0 s2 x, B2 T; B! k! of cities increase. Formulations ; 6 b) f$ q. F8 n1 w0 M7 S4 K; T! with more than a dozen cities ; 8 x6 z8 S- l% Y% R2 r1 n/ z! WILL NOT SOLVE in a reasonable ; ; B- V+ F, `# ~, G$ }' X( d; A3 Z! amount of time! ; ' F* W) E7 v) d$ Z!************************************;+ C. N( ?- u3 W
9 Q9 w3 h; a( @: s. K SETS: 0 a z4 c1 V0 p" E* C2 c9 |8 T ! Q(I) is the amount required at city I, / L! w; F; A- w% S/ F) w5 Q6 l8 U U(I) is the accumulated delivers at city I ;/ Y% M" ?! `. x* I
CITY/1..8/: Q, U;( v* c: P3 r" @
7 O9 w6 J, @- B$ k7 K; V ! DIST(I,J) is the distance from city I to city J # @, Q8 O4 z2 p( i W/ e1 U X(I,J) is 0-1 variable: It is 1 if some vehicle * o1 p9 z, e" y) {2 U9 I2 k travels from city I to J, 0 if none; D0 k5 P* b) b! A, @ CXC( CITY, CITY): DIST, X;4 ~5 @ z; |* }* |+ L
ENDSETS2 t9 [5 s1 m! }
( w- u& g- r5 L/ A1 ]! W w DATA: t, @' R7 B- Z; I9 a ! city 1 represent the common depo;7 F( L7 B, h* ?8 u; x
Q = 0 6 3 7 7 18 4 5;4 J& a5 w/ u# M0 M6 @( H# L
+ y5 O3 o9 @: w5 K+ q- A ! distance from city I to city J is same from city " s g: t. f3 n; ^ J to city I distance from city I to the depot is$ p$ \' O6 d5 o. ]( m
0, since the vehicle has to return to the depot; y8 _" `8 R ~4 J4 j# ~1 j 3 O9 V1 g7 E' D; _$ N! C5 ~$ l0 h3 u DIST = ! To City;4 @' C6 F4 s) E6 O: M& G
! Chi Den Frsn Hous KC LA Oakl Anah From; ( U+ o( A/ Y* b 0 996 2162 1067 499 2054 2134 2050!Chicago; 4 _8 I" |$ P9 C4 f; C, J 0 0 1167 1019 596 1059 1227 1055!Denver;1 `6 \* R% _( k+ \3 r
0 1167 0 1747 1723 214 168 250!Fresno; 7 k9 H5 _8 `; u7 K" k# V1 R 0 1019 1747 0 710 1538 1904 1528!Houston; ; Z5 @) {3 \7 k- l% g 0 596 1723 710 0 1589 1827 1579!K. City;. Y/ L: l6 _4 w; S
0 1059 214 1538 1589 0 371 36!L. A.; 6 @& q3 ^* B, M& T 0 1227 168 1904 1827 371 0 407!Oakland; ) K# k2 s- _; }3 b- z4 ? 0 1055 250 1528 1579 36 407 0;!Anaheim; 5 ?$ s8 i% `1 }2 J, R8 a, X/ u% M( \1 |" A* A
! VCAP is the capacity of a vehicle ; K% S1 K: y2 I2 m/ X8 J, @
VCAP = 18;2 J% j" A2 z3 h6 [: n
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! Minimize total travel distance;! H" P' V; C2 w/ \1 B, m
MIN = @SUM( CXC: DIST * X); 4 r1 Q6 G8 z& `4 B# { w2 D$ R+ g. N2 N/ G8 m- k8 M; {
! For each city, except depot....; + g, r: j2 x( b) P( m/ F8 |9 I @FOR( CITY( K)| K #GT# 1: - \% l9 d; [0 b2 e) B1 z8 b( q, y$ `+ p/ h" Z' w
! a vehicle does not travel inside itself,...;! v8 y( T: }- F3 X! I- `, F, Q
X( K, K) = 0; 0 ], ~& E7 W! _7 y0 i) G. I i5 g* B7 J; V" M
! a vehicle must enter it,... ; ) e* p* w. `8 O9 _( p) I1 G; u @SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR# / T4 x. _. p! d Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;9 i, i* c; r0 F1 i
7 G* J# a+ }2 e; W0 J- f. C5 u ! a vehicle must leave it after service ; 2 l( k. h9 i4 O. Q9 W @SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#2 [( Z2 K4 w0 ^( |7 z; e
Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1; & X7 n) R8 G- q* j, b' v) } ; W! Z4 d- X6 j) n& { ! U( K) is at least amount needed at K but can't S/ C' q" X# Z! `9 C0 m exceed capacity;1 n( z6 z, s: N9 g8 V; G( O# c
@BND( Q( K), U( K), VCAP); : g/ a& l8 e" e9 y" K" R0 E$ e2 w) z6 w7 P
! If K follows I, then can bound U( K) - U( I); 3 F8 _. b9 i4 z1 [7 O5 W @FOR( CITY( I)| I #NE# K #AND# I #NE# 1: * c) k8 w b' }7 l+ D. A7 b, [) L+ @
U( K) >= U( I) + Q( K) - VCAP + VCAP * # n$ A& s* I5 R6 M: U& U ( X( K, I) + X( I, K)) - ( Q( K) + Q( I)) * I: P! _1 i; W& y6 v" |- V& K * X( K, I);6 U2 Y/ m' H) C$ l
); % p5 \1 J1 ^+ ^0 D" D. M8 \ z . S. a0 t) {" a ! If K is 1st stop, then U( K) = Q( K);# d" K) \6 U5 u
U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K); P( W4 `' R) `! O) a7 E( u8 f- s$ U ( `' G/ f; a7 h ! If K is not 1st stop...; 4 ~5 T# w; M' F. i8 d U( K)>= Q( K)+ @SUM( CITY( I)| : E v1 g. U: h I #GT# 1: Q( I) * X( I, K));7 g# W/ ^7 R: F! i( {5 S$ q# q
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