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MODEL:
9 H# p6 t/ d" c# g( v9 }
0 ~( ]7 R$ a! j! The Vehicle Routing Problem (VRP); ! I4 ]! K. [4 x @* d
3 R% Q) z6 {1 J!************************************; G2 x3 z- g& S& m
! WARNING: Runtimes for this model ;* p4 ~. G9 _6 P, Y. _$ U
! increase dramatically as the number;
Q' ^6 V' c: f3 F- z3 Z) j! of cities increase. Formulations ;
: T0 r( w9 U1 a3 o! A. L! with more than a dozen cities ;9 I/ I* r% Y$ G" g
! WILL NOT SOLVE in a reasonable ;' `0 e$ G/ q! z6 @
! amount of time! ;5 K g4 ?! Z5 U) y" l& r, g
!************************************;$ E! g) H& f' u& \9 ~; X9 N
* G+ e( X8 c7 ?" k0 h, z# f+ x SETS:8 m3 H @" V/ c( M" O% Y& a8 N
! Q(I) is the amount required at city I,
; [& @" L" F' X% U3 U U(I) is the accumulated delivers at city I ;, s9 E* o( N5 g7 ~7 H9 a
CITY/1..8/: Q, U;8 f) t- }/ y1 [2 `' m
7 B2 h. d5 d: V2 X2 C: n8 j ! DIST(I,J) is the distance from city I to city J
1 U8 V( ^2 `' H9 B# X X(I,J) is 0-1 variable: It is 1 if some vehicle
# o& C9 [5 h6 d' ?1 P; O! k travels from city I to J, 0 if none;) @ k, @6 r# A ]& u4 H" Q* W' Z
CXC( CITY, CITY): DIST, X;, Z* a+ S0 o+ {7 ~& v! u
ENDSETS
1 v$ T3 H$ x0 x3 @6 O, @5 B6 Q# l4 C& b3 e
DATA:
" s/ @6 \. i! d6 N5 |1 A0 U ! city 1 represent the common depo;
, j% |) E4 @5 R; u2 j& B2 X7 a Q = 0 6 3 7 7 18 4 5;3 Y. ^) w E" a# o/ j
. R; R) f H. f5 P7 J ! distance from city I to city J is same from city
& b' x$ ~, o. S2 Q8 o$ |! Q( w |" D J to city I distance from city I to the depot is0 z: f# d8 {1 x: n5 V9 C6 s
0, since the vehicle has to return to the depot;
! G1 ~: T& R/ z1 {- _" m
N5 d: U/ S y- {8 R. [$ T DIST = ! To City;
% T( i; [. l% J ! Chi Den Frsn Hous KC LA Oakl Anah From;
" Q( u- F3 G( z( u+ V) H7 H 0 996 2162 1067 499 2054 2134 2050!Chicago;+ |1 P& C% R, V4 p* @
0 0 1167 1019 596 1059 1227 1055!Denver;
4 B; L$ ^1 q6 V2 c 0 1167 0 1747 1723 214 168 250!Fresno;2 v- m5 Q, l. T7 g3 ~/ o
0 1019 1747 0 710 1538 1904 1528!Houston;
, s* A$ p0 o h! h) M 0 596 1723 710 0 1589 1827 1579!K. City;2 I: B* [+ v; v6 Y8 o
0 1059 214 1538 1589 0 371 36!L. A.;
! y7 e$ e9 C! H& G; f3 z 0 1227 168 1904 1827 371 0 407!Oakland;
4 d# t0 v1 b$ ]/ T) ]) M! x 0 1055 250 1528 1579 36 407 0;!Anaheim;
# [3 B% r6 m5 t0 K1 @+ w2 T+ E# T" x2 ?& P8 S
! VCAP is the capacity of a vehicle ;
" Y! ^. J3 j% J4 A VCAP = 18;2 K' y5 D8 q: ~9 {2 k
ENDDATA
8 e2 @+ o! T/ w0 b# Z1 C2 r
) U3 \, r/ n K _2 q5 K ! Minimize total travel distance;
' M) M* n+ f1 P+ R/ e# H @ MIN = @SUM( CXC: DIST * X);
2 K" e$ P2 }" S; B/ G/ Q: h7 f2 k0 W! o X1 |. I/ L' c* T9 M6 {! |
! For each city, except depot....;
; h" n# o( i8 R' H* F5 e; H" } @FOR( CITY( K)| K #GT# 1:9 [: V. M4 J7 ~ s9 I0 c" h
) C6 Y: y: K* \$ _' T* B
! a vehicle does not travel inside itself,...;
5 P! M: N1 Q( {9 F5 B9 p X( K, K) = 0;2 \, y- h- g# j8 L
5 e& C ~6 x' X: ^7 M
! a vehicle must enter it,... ;
$ B3 i+ X- A- F) R: \, W. T @SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#
, g$ S. o1 t6 p& R7 R5 d! C- _ Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;4 T. w9 u1 v" o; F
- k/ f8 \8 q C& O2 T9 H! [" g) c
! a vehicle must leave it after service ;
" s3 P `$ R. I* @7 t. x @SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#
' p/ J; L' m" l7 ^( s) b) u Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;2 D; \" F5 w% w( u$ D( F
0 p z: P& q+ n9 `5 \7 J# u% ? ! U( K) is at least amount needed at K but can't : e+ [: N) M0 _8 I9 ?
exceed capacity;- V5 I0 b. k; {/ {6 N" ~. ^+ p
@BND( Q( K), U( K), VCAP);
+ B$ b6 z& N) k" m6 f; o. k
4 x2 r1 a% a! G F5 } ! If K follows I, then can bound U( K) - U( I);
" q {: C6 c y: G+ e1 `+ Y @FOR( CITY( I)| I #NE# K #AND# I #NE# 1: ' K- a3 f* Z: f
U( K) >= U( I) + Q( K) - VCAP + VCAP *
& z9 V0 f7 _' V3 F4 @. C ( X( K, I) + X( I, K)) - ( Q( K) + Q( I)): S- o' I% I/ R3 G. H$ }; V$ `8 S0 L
* X( K, I);
3 R8 B! k6 \7 _8 ~- B );0 }" }$ t+ N! d9 e8 Z
/ g6 F# l" M6 L: Q6 h4 G- S$ m
! If K is 1st stop, then U( K) = Q( K);2 K$ h2 w5 m. c" o. m
U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);
( |, t; L1 z$ T( d* C# G" ] u# f- m$ ?& ~" F
! If K is not 1st stop...;
2 n1 B# v7 @4 D U( K)>= Q( K)+ @SUM( CITY( I)|
/ E7 R9 d; Z( y4 `# G I #GT# 1: Q( I) * X( I, K));! V0 P; V' Y+ U6 C1 `
);: K0 ?8 k$ h) J( L, e8 W4 b
& p; Q; p7 F% M7 r5 t/ A% I* d
! Make the X's binary;" i9 e9 z- O! [0 {2 z$ w4 v
@FOR( CXC: @BIN( X));$ b$ x9 N6 q& y" w$ ~' E. j
( Q# @$ a. I3 f( P0 ]6 Y6 q4 m' u) q
! Minimum no. vehicles required, fractional + T3 ]8 A, B$ B# ^9 x9 y
and rounded;% ^$ \1 K' E& I8 A* T$ ~: x! M
VEHCLF = @SUM( CITY( I)| I #GT# 1: Q( I))/ VCAP;- v/ S2 B, z& R/ j/ A
VEHCLR = VEHCLF + 1.999 - * M6 N) m$ m/ B* C4 t
@WRAP( VEHCLF - .001, 1);9 x: M( k* [, {, w
7 M t5 \6 t1 B/ t4 k* d: {
! Must send enough vehicles out of depot;
( q! @( Y# \9 {: b8 `+ ?* |, O$ W @SUM( CITY( J)| J #GT# 1: X( 1, J)) >= VEHCLR;6 N( c4 c) m5 \! r0 e' y7 p [( g
END
# K! J4 }, |1 ~ 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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