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MODEL:4 _: W b" ^: |8 P# R
8 f! \; W3 ~6 S4 D6 }! The Vehicle Routing Problem (VRP); 1 b% x* q5 B0 C" K; E
2 p2 e0 ?- _ H5 O!************************************;! `8 [$ T- y4 d/ _. K0 P3 a
! WARNING: Runtimes for this model ;
" U( ^" j6 s9 i+ S1 ~% G, l! increase dramatically as the number;' ?! C' r" ^) H; l7 y4 _
! of cities increase. Formulations ;
. B( l2 q( W6 i* D6 Y5 s! with more than a dozen cities ;' k1 S- X( r4 U' E
! WILL NOT SOLVE in a reasonable ;
0 I* g# b8 `6 E4 Y* ~7 y! amount of time! ;
4 f' s6 N& f5 j: m7 E3 A!************************************;4 `6 W' q% p. E8 g, m
. }+ t H# {; O8 ]$ z; e SETS:
6 J1 V+ d1 _ c: {2 ?0 S! o6 x; _! f ! Q(I) is the amount required at city I,, y5 Y" B5 W/ p: k' p
U(I) is the accumulated delivers at city I ;
, w2 Z1 N7 ^5 ]! c9 W CITY/1..8/: Q, U;8 G2 L9 K& \ B+ `
( |7 V5 V+ b9 X7 j. I2 q
! DIST(I,J) is the distance from city I to city J( Z1 F0 R; N& B, a3 j5 W
X(I,J) is 0-1 variable: It is 1 if some vehicle3 Q! {! o1 N# U0 |1 e$ I; j
travels from city I to J, 0 if none;
& W9 U2 j T6 S' I CXC( CITY, CITY): DIST, X;
; f: _1 E1 l- C' m5 C0 {/ K5 N9 l ENDSETS% B8 c' S) M9 q) l
* b2 ^! Z6 d/ M; q$ y( }
DATA:
/ e* r. N- Z! G! Q% W" x, } ! city 1 represent the common depo;
s$ [% V5 I G0 K) i: d Q = 0 6 3 7 7 18 4 5;
, {5 \, d/ v6 E+ }' l" d" a, H+ `
# ~/ y1 g1 d, j3 K2 |! m4 s) I2 }* Y ! distance from city I to city J is same from city" t( H: a3 Q" o! O6 n5 I- x8 b3 E" n5 ?
J to city I distance from city I to the depot is
0 c4 I; I3 i1 W* S( P) [ 0, since the vehicle has to return to the depot;
; v2 O8 g9 Z- i# @4 G3 R+ T6 N* D( K6 n$ U; v, l2 n S$ [
DIST = ! To City;
; g' m) u- L; e, m8 o% I7 O9 L ! Chi Den Frsn Hous KC LA Oakl Anah From;. C) j! O* }+ Y4 E. U5 w! q7 D
0 996 2162 1067 499 2054 2134 2050!Chicago;) H" D. q: X, h$ {: q! P2 G2 R
0 0 1167 1019 596 1059 1227 1055!Denver;
! |# I1 E- {+ \, Z% b+ w 0 1167 0 1747 1723 214 168 250!Fresno;
7 [, b6 f1 i8 b 0 1019 1747 0 710 1538 1904 1528!Houston;
; x' H" ^1 l& ^8 r" o1 d. F 0 596 1723 710 0 1589 1827 1579!K. City;( `! P4 n, S& u6 l% {! U: R, ` E
0 1059 214 1538 1589 0 371 36!L. A.;. h: e* ]0 ~' |1 j2 A
0 1227 168 1904 1827 371 0 407!Oakland;. e O' \2 k+ q. M
0 1055 250 1528 1579 36 407 0;!Anaheim;' n( E5 s) m g% {4 g
7 u# V+ ^( y% l+ F$ C# {5 |) { ! VCAP is the capacity of a vehicle ;# l4 c6 A3 m! A3 {' _5 {
VCAP = 18;
6 N: I$ I5 s: ^ ENDDATA" _0 q6 s+ I$ R! g4 b7 K# ]
# X, T. `0 O4 E6 J5 J& K$ \
! Minimize total travel distance;
3 k0 ?6 }9 P/ y- P: x, c MIN = @SUM( CXC: DIST * X);
, r! n+ @/ E1 j# z6 q( d2 N8 e
1 y8 a( S8 r# b3 N4 w+ ? ! For each city, except depot....;' x# @7 }9 q* [
@FOR( CITY( K)| K #GT# 1:
$ C3 V% [5 v& h- o) j
1 z$ e( e+ M- ?" R* D( Q0 t ! a vehicle does not travel inside itself,...;
# {$ D) d2 h$ S/ R) w# p2 f! x8 Y X( K, K) = 0;
( P8 N, g, j1 y+ I7 e( g# u! }4 B9 a! f1 L5 o2 M
! a vehicle must enter it,... ;. H( s' ] y" t$ f
@SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#
; _, o# m3 |3 n% ^8 ` Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;" \5 G7 O5 J: L0 w# I7 v
' y" M3 f4 [/ X9 \& P: R- t
! a vehicle must leave it after service ;6 I) t% {1 T# y
@SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#5 @, E* y) S: _# [2 i" Y+ }
Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;
0 n1 I2 L U, z0 f1 U- g0 ~
/ |3 x3 J3 K' J6 Q) T/ u ! U( K) is at least amount needed at K but can't
1 \! D% b& o! J exceed capacity;$ b; M3 h* ?; ^3 R2 e
@BND( Q( K), U( K), VCAP);. Q. h! t) M" M6 t
. ]) z+ e5 O0 u5 m5 m( d1 ?7 W
! If K follows I, then can bound U( K) - U( I);. U1 b, r$ I( P" G% `3 l
@FOR( CITY( I)| I #NE# K #AND# I #NE# 1: / n- \: _" i7 u$ z1 E* m+ a
U( K) >= U( I) + Q( K) - VCAP + VCAP * * T8 ], Z' F5 W8 h7 D
( X( K, I) + X( I, K)) - ( Q( K) + Q( I))
' H$ c# G* z3 r' n* v) H * X( K, I);
$ ~/ W/ ?2 p8 y( m) M3 x3 J% {% ] );0 B5 o& N( F; K, N: W: A) S7 h l
/ ]: N+ m6 @# l0 H$ K8 ^. M; e
! If K is 1st stop, then U( K) = Q( K);
8 y; M' a' \$ i* G U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);
6 H! \! Z( A, n5 D8 A1 f+ {5 g% L; ?6 k/ E7 ^+ D B5 L$ v
! If K is not 1st stop...;' E, U& x/ P- t5 J
U( K)>= Q( K)+ @SUM( CITY( I)| % N* y7 l S+ b/ L8 w
I #GT# 1: Q( I) * X( I, K));
7 F) X+ Y6 _ M3 U" H# x, W );
" H/ `- w7 L# }% m% g8 I2 y( A. y" a6 m
! Make the X's binary;
! b- r3 {! j, v6 M1 f4 f4 g @FOR( CXC: @BIN( X));
- _; v( }/ x: V
0 [- F) o% n" l/ |/ X ! Minimum no. vehicles required, fractional 8 U# V: D+ w7 M
and rounded;
; K W7 W8 g# H% ? VEHCLF = @SUM( CITY( I)| I #GT# 1: Q( I))/ VCAP;# d# f# D4 t) i; b5 d' ]' p- v3 c9 H) |
VEHCLR = VEHCLF + 1.999 - 0 K0 N0 t4 s4 N* ^$ G
@WRAP( VEHCLF - .001, 1);
/ [. J6 _. J$ t1 I" L. K# a. c; y2 a$ F
! Must send enough vehicles out of depot;& l% \" b/ Y; d5 E! L- T
@SUM( CITY( J)| J #GT# 1: X( 1, J)) >= VEHCLR;& k) X- R3 Z( Q
END9 \: A6 N1 f0 O+ n' F( O* G
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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