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MODEL:1 s9 g" m# e u% W
: U" p9 C* m1 _1 W5 ~, R* Z5 l3 r
! The Vehicle Routing Problem (VRP); # { w6 o4 |. l6 x1 ]
& c' v% E/ x! ]( E; f
!************************************;
+ Y: x+ y% ?" _- N! WARNING: Runtimes for this model ;
$ t" Y5 Z. n7 \0 i8 }; p0 t! increase dramatically as the number; {5 K' A8 \: m9 v. ~
! of cities increase. Formulations ;: h6 J, r$ j8 F! m& e& o2 B5 y) u
! with more than a dozen cities ;: B$ w7 W6 |4 J9 }( [- \ C$ l
! WILL NOT SOLVE in a reasonable ;
0 k3 u5 c, ]" R- h. w3 G8 P! amount of time! ;
. E: s8 P$ o% z!************************************; @5 S" s0 Y% s" h8 |
+ ?; j' u" F( k- v* Q) L6 {
SETS:
' ]$ v, O5 _% u4 H6 ~2 A7 s ! Q(I) is the amount required at city I,( F( f6 o1 X( D" R: a% L8 n
U(I) is the accumulated delivers at city I ;
* I" U8 i: b% }; u' r0 F6 p CITY/1..8/: Q, U;4 y ?1 R- c4 C6 w8 P
( l- H: p0 t/ V/ j8 P; a ! DIST(I,J) is the distance from city I to city J& b, I+ c" s8 X/ h9 o" M
X(I,J) is 0-1 variable: It is 1 if some vehicle/ ]' o9 H% O* @& ]9 A
travels from city I to J, 0 if none;
4 ^4 K0 i5 o% k+ D+ m3 j2 | CXC( CITY, CITY): DIST, X;8 Y9 ^+ y6 w( C5 m# z' I
ENDSETS
: O( _/ D# C5 }+ I3 i1 V( f& s! W9 r0 H# V
DATA:- e# A: h$ _ ]% V, S1 U
! city 1 represent the common depo;
3 D' q+ V& ?6 U5 N' s& A5 X' ^; {; C Q = 0 6 3 7 7 18 4 5;$ h+ L! Y4 d$ Q# N' G
, @$ l# O3 w) U9 U: z$ O ! distance from city I to city J is same from city' h/ o! [* `) X1 i) b2 z2 H
J to city I distance from city I to the depot is# u8 A" Q$ l8 u; ^
0, since the vehicle has to return to the depot;6 }& j/ T6 u. b( @+ X1 i
9 k R& ]" T3 i4 C* V0 h/ r
DIST = ! To City;( o9 s3 v/ i0 l" q' d* o; {
! Chi Den Frsn Hous KC LA Oakl Anah From;
( y5 w4 b3 A8 o; I9 x 0 996 2162 1067 499 2054 2134 2050!Chicago;
X. G( |3 Z5 c) d, z: { 0 0 1167 1019 596 1059 1227 1055!Denver;
1 c. e8 F! w1 d6 m# F( O 0 1167 0 1747 1723 214 168 250!Fresno;
4 b: P' o% T; H( g+ w1 Z0 s: B; f$ a 0 1019 1747 0 710 1538 1904 1528!Houston;& ~1 R4 Y9 g4 k0 x$ K
0 596 1723 710 0 1589 1827 1579!K. City;; l% J! u7 u3 j% @
0 1059 214 1538 1589 0 371 36!L. A.;
+ V" I' ^( H3 r) k$ z- q 0 1227 168 1904 1827 371 0 407!Oakland;/ F* i/ z3 A r1 K) Q/ H
0 1055 250 1528 1579 36 407 0;!Anaheim;
6 i# V9 t0 z- d& }4 O. S) t
) V; k- Q# B& M# P- ^4 R2 M ! VCAP is the capacity of a vehicle ;/ g; I0 z+ l* x Z( C3 G
VCAP = 18;0 J( G" I* m3 K( g w2 ]0 U6 G
ENDDATA
1 z- _+ C7 q' T7 s$ V- H5 q2 C" D
! Minimize total travel distance;3 G: V/ _$ }* D1 l/ p/ Y
MIN = @SUM( CXC: DIST * X);
! f: ]6 [2 g( \; |9 [4 I2 N
4 Q- Z0 }2 _! u: B5 d" a ! For each city, except depot....;
# ]$ C' _$ J6 |2 z7 I @FOR( CITY( K)| K #GT# 1:; Q' Y- B u5 s
$ d2 v7 F8 A' ?) ^3 I7 i5 Y: G
! a vehicle does not travel inside itself,...;7 }6 d6 @# r+ H3 p$ q
X( K, K) = 0;
3 K. B/ ?$ `+ N6 o( W
- c8 E6 y% Y! B+ C" G$ k ! a vehicle must enter it,... ;
( r$ F! S2 h! A @SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#. [: i# B" G) Q
Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;
# F! h Y, p, Q3 q1 S& M! ^' r) ~, Z5 g! M% o
! a vehicle must leave it after service ;
# w5 C' g+ q# x @SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#% M% x$ ~) C7 U' s4 P& e9 \3 q
Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;
, ^- x6 A# K- a6 s2 V
- }6 O# _9 p2 e4 U/ C2 A7 w ! U( K) is at least amount needed at K but can't
" g( E) \! j3 y ?, Q( k# F exceed capacity;
$ p# C# k# r! Y0 P+ ]% a$ I @BND( Q( K), U( K), VCAP);: |1 l. {+ T% F+ d) X% X; q
$ f6 \% l/ E1 M8 ]8 c- B+ q
! If K follows I, then can bound U( K) - U( I);
3 h/ c. \0 I5 ^$ [! r0 d @FOR( CITY( I)| I #NE# K #AND# I #NE# 1: ' v2 j4 v8 Z, `- ^
U( K) >= U( I) + Q( K) - VCAP + VCAP *
# m; Z! D1 r3 k& ?7 J- t! X% ^ ( X( K, I) + X( I, K)) - ( Q( K) + Q( I))
- K& r5 A2 m9 A8 k * X( K, I);8 S9 H# }! ~; P) Q$ l
);1 P- i6 s' [3 ~+ |) H3 a1 X
& y: f4 L1 w' q0 o7 Q5 d ! If K is 1st stop, then U( K) = Q( K);7 H9 r7 Z4 S% C) K% v
U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);' L$ s/ y2 e4 M
: N/ D2 p7 Q' I
! If K is not 1st stop...;
8 T$ [& ~0 M3 t; i U( K)>= Q( K)+ @SUM( CITY( I)| & u$ X% H( K2 |. L
I #GT# 1: Q( I) * X( I, K));
& R3 E9 F# s9 A );! E/ @' b0 E' n4 m. ^+ a, n+ i. ^1 ?
* t" Q7 N* t( A0 x$ a# ]; | ! Make the X's binary;. |/ g( k8 C" x- d- f. \0 |9 D
@FOR( CXC: @BIN( X));
3 M r; e$ ]: N5 t% H0 H- G8 n6 T% A7 ]
! Minimum no. vehicles required, fractional 9 [2 M8 u, ~. p/ b; Y) }$ e
and rounded;
" P V( m0 g9 L+ d _ VEHCLF = @SUM( CITY( I)| I #GT# 1: Q( I))/ VCAP;
, u& `0 s$ Z6 B5 M+ c7 W2 \7 D' J VEHCLR = VEHCLF + 1.999 - 5 t) X8 t( N0 ?1 t- C2 i+ d1 l
@WRAP( VEHCLF - .001, 1);/ u: V. R0 A8 I1 c$ p; s
5 Y/ @/ |, T3 T" U ! Must send enough vehicles out of depot;9 N" h# ^5 m5 P& O( u
@SUM( CITY( J)| J #GT# 1: X( 1, J)) >= VEHCLR; T+ y y! I3 T* D0 m
END
+ C( C! i0 d7 l8 \; ^) l0 w 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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