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MODEL:2 ` Z( _9 R; g+ ?3 k
+ i- W7 ]+ Z. H6 w* R6 r2 h7 T, J
! The Vehicle Routing Problem (VRP); 8 J U1 o% g7 F
+ a. Q. N1 s: B1 b- K6 M!************************************;" u6 O0 U; S. }( j; B
! WARNING: Runtimes for this model ;
, X% M: C" w1 k# H: F! increase dramatically as the number;- c8 V# T3 R s% I8 e2 M
! of cities increase. Formulations ;$ l) }5 d. v' j3 j7 j
! with more than a dozen cities ;1 [& i: z6 S2 E: M) i$ |
! WILL NOT SOLVE in a reasonable ;
2 Z/ R, L) o- Z2 h& ^# [2 @! amount of time! ;
4 Q1 U' X" c; a!************************************;
0 n2 H3 S9 ]# E% v5 E% w" e1 m) Y$ K! z- `* h6 c
SETS:
$ g) T5 e: p: j* u ! Q(I) is the amount required at city I,9 y$ ^2 J+ Q& s( b: q' ]# D
U(I) is the accumulated delivers at city I ;8 n' K$ \4 z* o) z& N& l9 @
CITY/1..8/: Q, U;% _. g2 u1 ?* S* ?& X# b
4 E3 F7 Q! u5 C" j2 a
! DIST(I,J) is the distance from city I to city J& J" j- d+ S4 a! ~
X(I,J) is 0-1 variable: It is 1 if some vehicle! |* S; t7 L8 L' Q& L$ X
travels from city I to J, 0 if none;. q0 q- E. a0 s+ X) ~/ F s( n
CXC( CITY, CITY): DIST, X;
+ R8 h5 R; q* ?( F ENDSETS
0 F2 m+ {. z9 X& A% _, K+ _" V' x% V+ r6 t
DATA:3 ^6 Q" P( A5 t/ M. m1 w
! city 1 represent the common depo;$ ^$ `! z9 M0 n `& }
Q = 0 6 3 7 7 18 4 5;" H7 ]/ {+ d% q6 G" W
1 I! }0 \! [5 ? ! distance from city I to city J is same from city! i# E4 X: R* i' g# Y' k0 M) n
J to city I distance from city I to the depot is
$ G0 o/ {- _, t$ a% q+ | 0, since the vehicle has to return to the depot;" @# g0 d3 b3 l$ w1 w4 O: N
$ [* }8 d, `1 U& G
DIST = ! To City;$ z4 y; V6 j g8 h M6 f4 q
! Chi Den Frsn Hous KC LA Oakl Anah From;
6 e+ k- o$ C3 {7 J' O8 |( Z 0 996 2162 1067 499 2054 2134 2050!Chicago;$ \; f7 ^# p, l* N
0 0 1167 1019 596 1059 1227 1055!Denver;
4 `! E) @$ w ^2 E 0 1167 0 1747 1723 214 168 250!Fresno;# T G8 F. e- v4 o) {
0 1019 1747 0 710 1538 1904 1528!Houston;: \/ ^& G1 F9 B/ x
0 596 1723 710 0 1589 1827 1579!K. City; b8 B4 f2 f" X6 X: H, J+ _, m
0 1059 214 1538 1589 0 371 36!L. A.;+ U- m: H* h4 K1 @7 ?
0 1227 168 1904 1827 371 0 407!Oakland;- R, v/ H# ~' A b, J
0 1055 250 1528 1579 36 407 0;!Anaheim;
: k6 k! }& a0 R/ e
& l' ^0 b: k" y: e ! VCAP is the capacity of a vehicle ;+ B( C" v$ Z, _- J9 E3 I
VCAP = 18;
6 q! _* k Z; D/ I) o ENDDATA
" C& p* H z* J
3 O' B( Z2 Z* n" N# f* o ! Minimize total travel distance;
: Z0 F* H* d: d4 N# w MIN = @SUM( CXC: DIST * X);7 e5 }) ], x1 P8 D
! ?. V5 l! ^' M* K ! For each city, except depot....;" E5 M7 P$ c. d5 j) d5 v$ U8 L7 s
@FOR( CITY( K)| K #GT# 1:' U2 F3 J W1 y& z9 I
: t" w# R; I% c* t2 X5 G
! a vehicle does not travel inside itself,...;+ a+ D P2 I* f( a" r/ B ^
X( K, K) = 0;
' d# L6 {9 @/ o. \5 I2 z3 e7 V. j3 d- r; E/ e0 x: J6 x5 B! ]5 ^# e
! a vehicle must enter it,... ;1 Z" f0 ?, O: w' I' q/ j
@SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#1 w4 z; _9 @% R2 c7 v
Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;
4 H9 F0 ]; f3 @% {
' k0 I2 {1 M- a$ d. Q: G( O F* ?, u ! a vehicle must leave it after service ;
# Z4 ]$ h" K6 |- D @SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#
1 n+ `9 u K9 o Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;$ V# O8 z( l/ b% M8 _
. i b1 S- e4 j8 o+ W5 f
! U( K) is at least amount needed at K but can't
/ c; F9 i$ }8 \7 ]+ l f$ Z/ y( a exceed capacity;5 A* b' S+ h" ?/ p; n
@BND( Q( K), U( K), VCAP);
; l: U& u, M7 m# y/ W5 Q! B ]+ t% A: l- W7 E3 ^
! If K follows I, then can bound U( K) - U( I);
0 x' ]( W+ z9 i( t! K }; \8 R; e @FOR( CITY( I)| I #NE# K #AND# I #NE# 1:
' K7 j2 I! y5 L# J& @5 h U( K) >= U( I) + Q( K) - VCAP + VCAP * : q4 m- w! G6 i4 t
( X( K, I) + X( I, K)) - ( Q( K) + Q( I))5 t8 |1 A, _' ~7 M0 j v# m
* X( K, I);# d4 C, i `# c' k& Q- x6 {
);& d" c$ c7 M1 @4 p9 l
) ~: c8 b: H1 `+ f ! If K is 1st stop, then U( K) = Q( K);" \6 k0 s/ E4 }
U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);
' w. T/ K+ U0 n) O O$ J8 Z' i4 W' x+ _/ o3 e5 e# n* R# q
! If K is not 1st stop...;
$ Y& k, r4 F3 n4 g8 x( ?, l U( K)>= Q( K)+ @SUM( CITY( I)|
* Q$ e4 L4 V& J; H I #GT# 1: Q( I) * X( I, K));
% I9 w. D: g. c! ] );
4 ?: R$ |2 e5 s1 Q H- z0 r5 y9 [: x+ A; e
! Make the X's binary;, m5 R2 }* T) h+ t
@FOR( CXC: @BIN( X)); c- y1 }$ T( h
1 [- T' f! A* O- l" \ E$ M
! Minimum no. vehicles required, fractional
( p! B7 j% }: Q4 d& W; P and rounded;/ }- G6 _/ F6 j! m [+ z |
VEHCLF = @SUM( CITY( I)| I #GT# 1: Q( I))/ VCAP;' S# ]5 K" u8 {( s# S
VEHCLR = VEHCLF + 1.999 -
0 y$ r J- O* D& P; B @WRAP( VEHCLF - .001, 1);
% [ z U) \; s4 x4 E$ H4 M& k3 n% k3 p% _+ [3 m
! Must send enough vehicles out of depot;3 C% S+ s7 c4 J/ L( A7 E
@SUM( CITY( J)| J #GT# 1: X( 1, J)) >= VEHCLR;
& w9 S& z- U8 K }' L2 j+ Z END$ b/ |) v R' m) 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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