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MODEL:/ [' ~. a# y" L4 D) C1 {( |' ^
& B$ V) c3 T* V+ l l# p) P! The Vehicle Routing Problem (VRP);
4 f+ J5 l p# ]8 K) }4 \9 v' B4 r8 W2 i0 O: C2 _7 `5 z3 J
!************************************;
( g" c5 U, f& x6 w- @' I* D! WARNING: Runtimes for this model ;1 D1 _4 b' P& }
! increase dramatically as the number;/ I8 b, ]4 c( ?4 N0 ~) L" z9 v
! of cities increase. Formulations ;! y- T8 U; G. o/ y
! with more than a dozen cities ;1 i- M# Q' F# B$ O/ [
! WILL NOT SOLVE in a reasonable ;
! Z+ h2 `8 ]- }7 f! amount of time! ;6 ~! K& ] W' Y! S1 q5 r7 \
!************************************;) _& L3 f' h6 `& [8 f7 ]0 @
- ?- ~0 e6 m2 X+ }5 ` SETS:- m, J! z9 e) {/ ^+ n% L
! Q(I) is the amount required at city I,8 c9 x) l% J+ r1 H) K+ l$ a o. x
U(I) is the accumulated delivers at city I ;5 a! _; _9 N2 Z+ D9 U" u8 r
CITY/1..8/: Q, U;9 J8 n: ~4 K+ Q' M: Y
9 W" {/ w4 S. K- [. D1 v ! DIST(I,J) is the distance from city I to city J
) H3 j+ F6 {; Z X(I,J) is 0-1 variable: It is 1 if some vehicle
K/ u) E# c+ \$ s travels from city I to J, 0 if none;
. q# }6 R* j" R1 Y, a# G- p! ~ CXC( CITY, CITY): DIST, X;9 a: ?# U4 x7 F& z } S: ]
ENDSETS) Y% D3 d" n7 t; q( J7 B% d
" _ a) z) ~6 H2 g
DATA:- ^+ v3 D/ B7 X s' b& n- L, M3 h* t+ R
! city 1 represent the common depo;+ ^1 k+ T3 Y) ?# Q: K6 @- W# Q% K
Q = 0 6 3 7 7 18 4 5;
1 h+ |2 D6 h* E1 {6 C* p+ r; a! p7 R6 V9 e# H- H- Z, _8 D% ?
! distance from city I to city J is same from city$ }8 q; @6 M) w" d6 f2 C
J to city I distance from city I to the depot is: e- b# Z% @, }& J+ K4 A
0, since the vehicle has to return to the depot;
- V& a9 P% m; u% F+ X( ^* `% e! ]: {) Z8 C) ?* x! H
DIST = ! To City;
. T) x7 H0 t$ R. c) V' ` ! Chi Den Frsn Hous KC LA Oakl Anah From;
& C7 n1 N* I4 H8 X' i 0 996 2162 1067 499 2054 2134 2050!Chicago;
( M; Z0 j6 C4 \ 0 0 1167 1019 596 1059 1227 1055!Denver;" K7 f' |* d( a% W6 I; A) }
0 1167 0 1747 1723 214 168 250!Fresno;
8 b/ m: R9 x9 p, L 0 1019 1747 0 710 1538 1904 1528!Houston;
% V/ C7 |9 m6 @8 U7 [: ]* p 0 596 1723 710 0 1589 1827 1579!K. City;
* _/ [6 H }* p0 I0 S( X/ r3 _ 0 1059 214 1538 1589 0 371 36!L. A.;
3 Z) X9 X# k! I1 W, x) r" W+ h 0 1227 168 1904 1827 371 0 407!Oakland;
5 P' X( ~4 B) a# F1 x 0 1055 250 1528 1579 36 407 0;!Anaheim;
& z4 u- j; N" V! B: d* I' L A* w: m! {9 i: x
! VCAP is the capacity of a vehicle ;' C- w1 J3 l; t
VCAP = 18;0 t) x. x; f' R; W4 ?+ g
ENDDATA7 I' ~5 c% m" z% ?. q9 c
, k8 p0 @2 O* w4 S, v ! Minimize total travel distance;& N# [. x+ W7 W, m# N
MIN = @SUM( CXC: DIST * X);
7 m: y2 ~8 W/ k2 O2 x/ m8 |% n) L% o( d$ A
! For each city, except depot....;1 e. N& g) G$ a7 m: {. \4 y6 o
@FOR( CITY( K)| K #GT# 1:
% Q2 J2 H, T% X6 B$ \
4 d" z! J8 V/ N% D% h8 U7 C ! a vehicle does not travel inside itself,...;: z G- |, I8 t& w6 C0 Y
X( K, K) = 0;
7 o; R& x" t' }& _2 ~& O
G: ^5 V9 c' y! c9 v" s ! a vehicle must enter it,... ;
+ O! k! W$ Q4 d/ E' a: L! d3 f" [) {' } @SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#- L+ m6 ]. N7 s. K5 y J$ p {
Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;2 j8 e" s+ e, l( u9 t1 k) ]+ G; q
: `% ]' K8 K" F6 l9 q% x& |
! a vehicle must leave it after service ;- f2 _9 v+ M7 v* [" R
@SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR## u" k1 @1 k7 N% ^
Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;
$ c% K7 D* k" z2 Q/ I4 a% n; U V- O+ A3 f: T* e8 _, J
! U( K) is at least amount needed at K but can't
- E+ G( X+ T/ t- B- {) F8 `' R exceed capacity;
7 I) e2 g( ^6 h- P- t3 E+ k# @' A8 j @BND( Q( K), U( K), VCAP); A) q; G" H' }# H8 O, c4 _8 I
6 O3 e ?5 T3 `7 p* P( g) |
! If K follows I, then can bound U( K) - U( I);
, Z2 N" l! i! Y- g P @FOR( CITY( I)| I #NE# K #AND# I #NE# 1:
) N9 h; K; N7 N r9 ]1 L6 u4 ?% A3 V U( K) >= U( I) + Q( K) - VCAP + VCAP *
; E3 [, \0 R3 J" b/ Z2 G' L5 U5 ] ( X( K, I) + X( I, K)) - ( Q( K) + Q( I))
- c2 A1 c3 X! j3 c7 m3 t9 D * X( K, I);( {' n: X; s) b6 m. v) l' @
);; x, @4 u4 T/ q7 V4 H
' l" P8 o+ D; q. z9 U7 c1 t b ! If K is 1st stop, then U( K) = Q( K);+ m# @) O3 A, a2 }0 n8 L& b' g$ i; H5 P
U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);
% O/ Z; i6 {+ Q5 @: l9 i8 ^2 Y
$ p2 q$ Y; a) @ ! If K is not 1st stop...;4 E5 z0 ^. a! M8 I0 T/ P8 j! r- d* ]
U( K)>= Q( K)+ @SUM( CITY( I)|
5 ~+ G! L! U; T I #GT# 1: Q( I) * X( I, K));6 X- |0 Q/ ^8 M6 w* `$ l
);# y7 E! k; ^' J, e+ s4 I. ~2 X- y: s' F9 ?
- `& h# ]- A/ I0 t1 F- I
! Make the X's binary;1 i9 q) v* J. [- c# n2 _6 p! O
@FOR( CXC: @BIN( X));
. r. X2 l0 h6 W5 q0 k+ P; J1 s0 S' p1 @" e( t, ^. {) ~
! Minimum no. vehicles required, fractional ' [( G+ @, |: n5 [$ b' B$ g# W1 a) [
and rounded;
' o' I' l1 i; K$ D1 v VEHCLF = @SUM( CITY( I)| I #GT# 1: Q( I))/ VCAP;) V' a5 |. O g+ l7 i
VEHCLR = VEHCLF + 1.999 -
: D# \" W) Z: `3 _ @WRAP( VEHCLF - .001, 1);
% ~- P6 W3 b3 a# |6 q' Z
: j" u b; D1 F, @; t ! Must send enough vehicles out of depot;) [8 ^; k' I) s4 T/ A/ I/ ?' ?
@SUM( CITY( J)| J #GT# 1: X( 1, J)) >= VEHCLR;
8 z1 h; a! D2 \3 R! F END/ W1 _, L- i7 a( ? L8 p$ \( o0 T
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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