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MODEL:* G* z- Q3 O- I( |$ O) h
) T* j9 l; S, F& d. h& Z7 R# _; ]! The Vehicle Routing Problem (VRP); 5 e3 ~7 y; p8 i! _ c3 w
& B/ x& _5 F" A, R8 N
!************************************;
* Y J4 c7 P. e# o) h4 t7 v5 r! WARNING: Runtimes for this model ;) {. H) T( u/ r
! increase dramatically as the number;
! V) Y" [, S3 h' ?2 x: C; V! of cities increase. Formulations ;
* N! `( m; `- e' j: X E! with more than a dozen cities ;
* I8 @- z, }2 J- H8 r# d, Q$ v) r! WILL NOT SOLVE in a reasonable ;8 Y8 R0 f% I% O6 g
! amount of time! ;6 V7 O, v; z0 z4 f
!************************************;( O3 `+ I) u& M( ?
0 q4 Q) H# U# k' ]
SETS:$ d" N2 n+ b4 G9 y% v
! Q(I) is the amount required at city I,4 N7 i: ^1 Q( o- y9 u
U(I) is the accumulated delivers at city I ;( i( w% @" o* d2 w$ B9 r+ m
CITY/1..8/: Q, U;: _- y3 w( p8 S6 A; M& S0 n8 u
9 W7 s9 k- n/ K- q
! DIST(I,J) is the distance from city I to city J
! H3 M5 a7 _3 f& [- [* i X(I,J) is 0-1 variable: It is 1 if some vehicle
# d. I' C3 j' M v8 R6 ~. N travels from city I to J, 0 if none;
# i. d4 i; a" y$ a6 N" f7 B CXC( CITY, CITY): DIST, X;. b. c2 C- z6 W3 N) ^
ENDSETS4 ]# k8 d1 R) ~: d
* S; K$ _& u4 t$ A
DATA:4 [1 m, }8 J% e) m! M9 d
! city 1 represent the common depo;- r4 J& E$ t8 m4 I% ?/ y ~
Q = 0 6 3 7 7 18 4 5;
9 }; t. ^- R2 P- z; ^7 g
; a. e2 r2 q/ O; H% i ! distance from city I to city J is same from city
- V& `+ b( Y! ^# g2 k' W J to city I distance from city I to the depot is/ l2 x; ~3 U5 b
0, since the vehicle has to return to the depot;7 K. G7 T6 Z( s! M
' e/ | S6 y; ^, E, u4 \+ | DIST = ! To City;
1 k7 I) o. i& O7 T1 s9 m ! Chi Den Frsn Hous KC LA Oakl Anah From;" z, U+ t' d* b5 X: p
0 996 2162 1067 499 2054 2134 2050!Chicago;- M) t% {" S( j. v
0 0 1167 1019 596 1059 1227 1055!Denver;
. \: z {; \& I. W* G9 y* ? 0 1167 0 1747 1723 214 168 250!Fresno;
2 t* x' H3 _0 R/ ~% q' Z4 N& M 0 1019 1747 0 710 1538 1904 1528!Houston;4 z9 k& O( x( D
0 596 1723 710 0 1589 1827 1579!K. City;, {$ B j5 M! m3 a4 C
0 1059 214 1538 1589 0 371 36!L. A.;
: d/ q* s5 d D$ m1 ]8 [* r' n' t, \4 M 0 1227 168 1904 1827 371 0 407!Oakland;9 [+ J; _& y+ k( G0 D& l. c9 r
0 1055 250 1528 1579 36 407 0;!Anaheim;4 J" ?4 l% U4 F# u+ h( F% b
& M# a1 @: ^6 l2 r; p/ d! | ! VCAP is the capacity of a vehicle ;0 e" x* K5 y7 I1 _7 Q
VCAP = 18;! Y- U) u* P5 {& t7 T* C8 W: i
ENDDATA) s- i$ R# C, G/ i4 [. r( B
7 k# Q' ^8 a/ {2 R4 ]" d
! Minimize total travel distance;# p5 q/ ?1 g4 Z" r/ _8 f( T I
MIN = @SUM( CXC: DIST * X);- h) s, Y. L' ?/ q+ h+ U+ ]
9 o# ?* b. c6 K8 A& Y
! For each city, except depot....;
! v7 S& t" B3 p& a1 Y9 m/ ?# K @FOR( CITY( K)| K #GT# 1:
- `1 g* m) \* H0 H6 V: W+ N
1 q7 `+ d) S, U ! a vehicle does not travel inside itself,...;2 e' t$ n% s A! U/ Q$ [0 T
X( K, K) = 0;
" X& c( }, y, [" @8 q3 g' m e: r
& o m2 Q5 K V. x* n9 o ! a vehicle must enter it,... ;
) d& f8 X! P+ J7 m! ] @SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#: E8 ]# ]" A* i) Z1 N- N9 D& m
Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;
/ N& B6 S# y% Y5 r$ L* ]9 G( L+ [( d: E( n. a4 H- g
! a vehicle must leave it after service ;5 v$ c' k) @9 J# |
@SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#% ?. g+ k( `6 Q% Q: `
Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;! c3 C; _8 z V* X
6 u6 ~. |" F" g* h
! U( K) is at least amount needed at K but can't + k. A3 r: w/ s- t' U& z
exceed capacity;
7 J+ y% F0 P: C* x* ]" }" \- y* B @BND( Q( K), U( K), VCAP);2 e; g2 Z: ?! ?4 g4 U7 r/ y
7 R8 p2 b- g, O9 z5 e1 \
! If K follows I, then can bound U( K) - U( I);
/ s0 g n7 ^; \: J) U( B @FOR( CITY( I)| I #NE# K #AND# I #NE# 1:
d* H. A7 \2 s2 y- K" {1 D6 R2 c; l U( K) >= U( I) + Q( K) - VCAP + VCAP * ! e2 `0 p) ?% L/ K7 p# o- u
( X( K, I) + X( I, K)) - ( Q( K) + Q( I))
! V# ~9 ]" b1 d * X( K, I);) K# S1 r/ q3 `
);
7 J8 d8 U; Q) Q. x+ C2 K6 ]
: w# o/ y2 X, M6 l) E" G( G1 P# c ! If K is 1st stop, then U( K) = Q( K);
+ N+ t: L0 n) W) c U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);
1 o: A/ F) G3 \- Z. C L( ~! l4 U# w/ E' D% c+ q! O$ G4 p' ]5 ~
! If K is not 1st stop...;
1 U. v. b2 ?; F( t% |# O* t5 y U( K)>= Q( K)+ @SUM( CITY( I)|
5 v# {& _$ U# W% f: G1 Q1 g; C! k7 L I #GT# 1: Q( I) * X( I, K));
+ p4 d3 e9 |& b6 I );1 F0 M$ _* q$ Y$ J0 o+ y- Q5 X
. k8 ?& D+ w/ ~ i' C0 B9 M ! Make the X's binary;
. R/ u1 q* W; w3 o* r( _8 u @FOR( CXC: @BIN( X));# G' o% U: _; C. z4 ]% s/ L: p/ x& R
3 N8 ?/ k' y: S
! Minimum no. vehicles required, fractional $ {; N, w, B! m" S
and rounded;
! a+ Y$ k5 F( c; d, S( C* s VEHCLF = @SUM( CITY( I)| I #GT# 1: Q( I))/ VCAP;
! y+ Z$ S4 C; I VEHCLR = VEHCLF + 1.999 - 0 t* i+ \+ R) g2 |9 y
@WRAP( VEHCLF - .001, 1);
" ?1 }& {. R# ?3 d8 Y% T" H# X' e: `) u+ Z( n. v
! Must send enough vehicles out of depot;7 e& }4 Z2 u" A. h
@SUM( CITY( J)| J #GT# 1: X( 1, J)) >= VEHCLR;
# i) o0 D, _, Q3 t* J9 o END. a9 @9 r5 a: R# D
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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