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MODEL:9 _, s* ]1 x/ Y, e' |) I
7 G- p5 Y3 H) V7 X: k* C; ]+ {! The Vehicle Routing Problem (VRP);
# ~# V) t. p/ v7 A/ Q, s! [% u! y
1 {; x) @$ [0 K; L, N1 q7 k!************************************;+ Z- v5 \- ~; O. R: _- S" F
! WARNING: Runtimes for this model ;
( _+ K$ n/ M$ }6 w# t$ A% c! increase dramatically as the number;: a$ E3 f" L0 b4 F# t
! of cities increase. Formulations ;% q7 K( q, r0 ]
! with more than a dozen cities ;
' `& e4 b6 W4 g( v) c" R5 ]0 V! WILL NOT SOLVE in a reasonable ;5 i. p7 H& v- [! C
! amount of time! ;
3 @; ` l2 c6 t" [" x) [!************************************;
& {) h" z5 l1 o3 D5 b1 `) p
( Y1 R7 t7 _9 ~: `$ e& Z SETS:( Y# X$ a; L% O" c8 s
! Q(I) is the amount required at city I,
1 k6 P3 Q2 C9 ^+ T" U/ O# L U(I) is the accumulated delivers at city I ;9 H4 Q8 c1 D) x" O
CITY/1..8/: Q, U;3 o# _2 u# K6 k! S5 i1 x
; m) {; e- ^9 y% ~; b2 N: r2 z ! DIST(I,J) is the distance from city I to city J: d, z) {. d u& i4 q, b
X(I,J) is 0-1 variable: It is 1 if some vehicle
7 j! B+ {7 m9 F+ _0 d* J" [ travels from city I to J, 0 if none;4 n$ [ w; z) ?3 T
CXC( CITY, CITY): DIST, X;) ]& u3 G i1 p- E
ENDSETS& V, y7 Z9 T; @( L. O
; ^; L ?/ [. V( u3 ~ DATA:* D/ n% M6 ] [9 w* b2 O4 Z' K
! city 1 represent the common depo;* D) t6 ~% x1 e
Q = 0 6 3 7 7 18 4 5;
7 r4 `4 q4 W" L
' n7 C" |# q, h9 G: B3 { ! distance from city I to city J is same from city
( j4 T( @1 v$ \1 E3 T- `9 a& z* ~) r J to city I distance from city I to the depot is
- t% a! V" d7 V/ v3 E0 n( z8 K' D 0, since the vehicle has to return to the depot;
. [3 [& y+ a# w j
, V9 E0 N+ n$ o) X+ O, c DIST = ! To City;. z6 ^5 C4 S' Y; @' A" @
! Chi Den Frsn Hous KC LA Oakl Anah From;2 _5 u, ?4 _4 q3 ]7 D$ s+ d; q, {
0 996 2162 1067 499 2054 2134 2050!Chicago;7 d' K, d e+ k% k
0 0 1167 1019 596 1059 1227 1055!Denver;
9 i) e, U5 f) v" D* ?5 } 0 1167 0 1747 1723 214 168 250!Fresno;
% e' V* G, P1 w* e 0 1019 1747 0 710 1538 1904 1528!Houston;9 M' l) U7 M) N" ^( C! B
0 596 1723 710 0 1589 1827 1579!K. City;; a7 j" |+ x5 v& w% [" {% V
0 1059 214 1538 1589 0 371 36!L. A.;' E/ S. f+ F# E2 s9 w8 `: `/ W, D
0 1227 168 1904 1827 371 0 407!Oakland;: q6 Z7 i7 }/ w6 A" p7 j
0 1055 250 1528 1579 36 407 0;!Anaheim;$ V0 Z+ `. B/ K7 S1 x
5 q8 H" p6 v9 Q0 g1 Q! q ^# Y7 B2 f
! VCAP is the capacity of a vehicle ;7 J4 ?! P4 A$ x
VCAP = 18;
. z) _2 ?$ E- Q2 a8 ? ENDDATA& J) K1 m* {$ k8 \) t, Y0 q, h
9 T/ I3 n& H/ U! h) ? ! Minimize total travel distance;
2 Q& a7 R$ C" c: e/ C MIN = @SUM( CXC: DIST * X);
; _3 X' t- D. R! J0 E$ _& Y: X/ M7 s9 Z9 e
! For each city, except depot....;
& E8 D5 B* o+ w: r B: i1 V @FOR( CITY( K)| K #GT# 1:
) Q% P0 A' l" u( r Z5 i! n7 F5 k0 b d
! a vehicle does not travel inside itself,...;4 N+ K( V5 f: p* P1 s7 S N
X( K, K) = 0;
" w4 [8 U; h# d$ G" h+ R/ R f3 R' n& v+ r2 u( e8 B) u& D4 b
! a vehicle must enter it,... ;
1 c/ v, Z5 b% r; }! D @SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#
9 h/ d# t" p6 g- h' q5 i8 B0 l6 } Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;
( Q4 U! N* G$ m. ^+ Y( \! ^$ u1 i
- [& V' T7 v$ ? ! a vehicle must leave it after service ;
$ H, g) @& e8 |3 {5 v, I @SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#
( Q0 A+ }' @( J" i8 m: y, D V" F. l Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;
' x& f" C! ?- E- \0 I+ S
8 h% R' q0 N" k) Y# X2 D2 ]* `6 h ! U( K) is at least amount needed at K but can't ( }% r; a1 S; [, O0 A9 F
exceed capacity;
$ F! T# e6 D: ]5 h @BND( Q( K), U( K), VCAP);' Y6 E+ v7 ?+ t! i% b `9 [
3 K: j9 w% j: U! T
! If K follows I, then can bound U( K) - U( I);
( I, Z- J) t/ E) q5 ?% D @FOR( CITY( I)| I #NE# K #AND# I #NE# 1: & H$ T% p/ s( n
U( K) >= U( I) + Q( K) - VCAP + VCAP * , h h/ [& ^, E( ~% R1 e
( X( K, I) + X( I, K)) - ( Q( K) + Q( I))6 d: m$ `$ j9 n' O' U0 {) S
* X( K, I);
2 f1 ^0 ^, @( u$ U! V ?5 ~4 _ );" Z: x6 p2 r$ y* W
/ Y% I; B6 e; ]# F8 F% g; }
! If K is 1st stop, then U( K) = Q( K);
1 {; X! ]( X" A0 P U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);
# ?, I6 K9 W: p; z7 Q# m9 u( G, T+ t. I ^, l' E
! If K is not 1st stop...;
, ]; C; l. p3 D& f U( K)>= Q( K)+ @SUM( CITY( I)|
* n d" B6 o) z& o I #GT# 1: Q( I) * X( I, K));
8 ~; |/ F. M6 c1 }8 f2 r. i; Y! { );7 z* \* F( q) h) [; I
( Y& T& w+ `* ~! A# [" A
! Make the X's binary;9 z1 ?. L$ @6 W
@FOR( CXC: @BIN( X));
1 z- V, y" g0 K1 z( r8 v9 a
4 m9 h% I" S1 h$ ~, }( }$ a ! Minimum no. vehicles required, fractional
2 ?, F1 f% {0 {- d3 l& K and rounded;5 o, B+ C* L' @/ P9 C
VEHCLF = @SUM( CITY( I)| I #GT# 1: Q( I))/ VCAP;- j- i1 D) k: T2 h7 \$ N2 j/ x/ J
VEHCLR = VEHCLF + 1.999 -
$ r( a. ?+ L; ^. c @WRAP( VEHCLF - .001, 1);
7 Z4 r2 R9 p& K" O0 y0 L3 e4 m( _5 C1 ^, |# X: J
! Must send enough vehicles out of depot;+ [6 j8 D! {2 p: {* u
@SUM( CITY( J)| J #GT# 1: X( 1, J)) >= VEHCLR;0 j% e1 V5 T3 I6 s4 n
END
- b; W# I6 U4 G$ p, J2 P 请问大家里面U(I)的公式如何理解啊 U(I)是城市I 的累积交付量么?谢谢 |
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