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MODEL:9 ~2 Y# b' m' [ a" Q# `% P
( R/ A! q: s6 e6 P5 U9 [! The Vehicle Routing Problem (VRP);
3 {' X2 s1 X2 t7 D/ |! ^! B, r' ?0 {" a6 y# L
!************************************;
' a; E f* H' w/ k& W, d N! WARNING: Runtimes for this model ;% I4 W" Y: A3 W" w& P# Y! @- b
! increase dramatically as the number;
7 H1 Z5 l! M4 A7 m) s% T2 {! of cities increase. Formulations ;3 y: l9 k+ Z* V$ ]1 z3 O
! with more than a dozen cities ;
: d. Y, h2 M: P3 [! WILL NOT SOLVE in a reasonable ;0 ` q# m; d# C9 n
! amount of time! ;
/ Y* O ?+ ^( Z" }! o) L9 n!************************************;$ n6 k. g2 h( y! k, p& c
9 M: h' q: [4 X1 B1 i! d2 {
SETS:* l8 |' ]6 Y3 }* ]0 b
! Q(I) is the amount required at city I,+ e! C+ p @$ |3 p
U(I) is the accumulated delivers at city I ;
# _; \6 y. ]% G5 {8 d9 o. v" a CITY/1..8/: Q, U;
: I5 s% e" \7 P8 \- Z5 D+ n" w5 C( P N1 C1 V" Z! }
! DIST(I,J) is the distance from city I to city J ^: P0 {8 k o- H8 u/ ?! h
X(I,J) is 0-1 variable: It is 1 if some vehicle0 |, J7 B$ S: w& h3 V: g
travels from city I to J, 0 if none;
; b& l# H. S2 q1 M5 N m CXC( CITY, CITY): DIST, X;
. t* J) S. h% h; O) S) c ENDSETS; l$ |/ n2 L+ m2 V8 X+ | @7 ~: A
6 f/ l+ p/ I& ~4 k
DATA:
6 C' K) @- K3 T: W f( A V& F ! city 1 represent the common depo;! t% |$ ^1 N7 _; ?( l2 p- x$ h
Q = 0 6 3 7 7 18 4 5;- }3 M5 _+ w3 O! x; H9 Q3 B
4 e4 E; n4 J: e0 r7 e" z9 f
! distance from city I to city J is same from city
+ G' L6 Y' I2 B" M# @0 x J to city I distance from city I to the depot is
5 o5 |; f' F( F: w( [) r 0, since the vehicle has to return to the depot;
7 X6 J5 P( v; f
+ g: E. |" u( x2 t& n( R& J# y DIST = ! To City;
$ A+ M/ d& s$ L( n! x' s* F ! Chi Den Frsn Hous KC LA Oakl Anah From;: `8 N8 G1 w5 c! @5 p9 x9 \
0 996 2162 1067 499 2054 2134 2050!Chicago;
& B! r; }* C7 K/ ^8 i+ q 0 0 1167 1019 596 1059 1227 1055!Denver;" t7 [$ f H* O
0 1167 0 1747 1723 214 168 250!Fresno;
2 E d+ F4 Y& k+ D+ ]# k. P) j 0 1019 1747 0 710 1538 1904 1528!Houston;, f4 w+ k0 C ^) k+ q: ?6 E( {
0 596 1723 710 0 1589 1827 1579!K. City;
! \- e. s; m. u- E8 v, O, c 0 1059 214 1538 1589 0 371 36!L. A.;
& H0 X8 m/ g$ f; e9 u* Y/ h# i 0 1227 168 1904 1827 371 0 407!Oakland;; e$ @' I- Q. y3 _
0 1055 250 1528 1579 36 407 0;!Anaheim;9 k; j5 S2 q0 o; Z3 j `' {9 ]- r8 ~
* ?' g/ t% C! @0 t: I% H' q3 \, q$ m; ? ! VCAP is the capacity of a vehicle ;
% Z0 M8 j2 s% ?1 u/ n VCAP = 18;0 M7 S- |9 v$ h8 E0 x4 w4 j) y2 s
ENDDATA
' I# y9 O' h/ g1 I6 g
7 R$ @$ u: ^& m7 I5 r. x; M ! Minimize total travel distance;) O* c( M& n' R. y/ I4 Q8 e2 `3 G& d
MIN = @SUM( CXC: DIST * X);* ~( z& w3 a: `9 P' ?
. W( Z; V* P# s# j/ v
! For each city, except depot....;
% n* k! H6 ~6 M. U" ^. [ @FOR( CITY( K)| K #GT# 1:# o6 U( P+ y& G3 G; j* p5 }
6 R( Q0 h, |5 o ! a vehicle does not travel inside itself,...;
% Y1 h: x& n: ] X( K, K) = 0;
* i9 t! ?+ q5 o4 s+ S8 q: D; k
! a vehicle must enter it,... ;& _- g& h8 l" V
@SUM( CITY( I)| I #NE# K #AND# ( I #EQ# 1 #OR#: b* k& r2 z- X, a4 n
Q( I) + Q( K) #LE# VCAP): X( I, K)) = 1;* `, a/ {- f* `7 I, y
* g" m. U1 | R. ~ ! a vehicle must leave it after service ;8 L3 S& j9 i% E) t4 J5 b
@SUM( CITY( J)| J #NE# K #AND# ( J #EQ# 1 #OR#0 c6 I, n" D# H4 p
Q( J) + Q( K) #LE# VCAP): X( K, J)) = 1;" S6 w+ c$ c6 |* ~# u
8 D/ V1 {% @) G: B ! U( K) is at least amount needed at K but can't $ y6 Y/ ^- l5 C9 Z0 j
exceed capacity;) V; f& g7 X! E
@BND( Q( K), U( K), VCAP);
% Y$ h4 U# j7 p9 A
2 f p8 `2 M" P8 P3 |% r, G$ f ! If K follows I, then can bound U( K) - U( I);9 o( w1 T3 R. @, K
@FOR( CITY( I)| I #NE# K #AND# I #NE# 1: , M0 n7 t! ^4 N! ]
U( K) >= U( I) + Q( K) - VCAP + VCAP *
R7 z* y7 q: | ( X( K, I) + X( I, K)) - ( Q( K) + Q( I))/ X- x9 C8 B7 z: [$ z- Z
* X( K, I);* ~9 ~) H) ]$ \3 R5 u. u
);
F7 S, Q3 F; v3 r2 B+ m( F B d; l+ b3 t" K& m
! If K is 1st stop, then U( K) = Q( K);
" z) u7 O7 i1 l8 C8 Y U( K) <= VCAP - ( VCAP - Q( K)) * X( 1, K);
( [ C2 O2 w0 \) V0 P6 |: O
2 Z. A* B6 w6 L( H8 N ! If K is not 1st stop...;
5 ?6 T% F5 J; U- f0 { U( K)>= Q( K)+ @SUM( CITY( I)|
3 t( |7 m2 X" w9 b I #GT# 1: Q( I) * X( I, K));
5 B- c* O, P: m );
" r1 j/ c) _7 K0 x7 @# m, G2 D8 o( z2 r: }7 u. w& e
! Make the X's binary;
/ T; s/ c M4 v! t$ O3 ~+ ~ @FOR( CXC: @BIN( X));
2 K8 R: m* O( {' l0 w, ^. ^; G; }" t* a' h( G
! Minimum no. vehicles required, fractional
) T' M. {* C d {* F% @! X4 d7 n and rounded;
; v2 G. w$ ?* ]" ~ VEHCLF = @SUM( CITY( I)| I #GT# 1: Q( I))/ VCAP;
; s5 {3 k2 L1 P$ r VEHCLR = VEHCLF + 1.999 - / {+ ^* a7 H7 C$ ~7 |2 ?* t
@WRAP( VEHCLF - .001, 1);8 t. V9 T* H% |. X
' B. R: w- L& ] V% o, t ! Must send enough vehicles out of depot;3 `( p/ n7 J- y
@SUM( CITY( J)| J #GT# 1: X( 1, J)) >= VEHCLR;
8 X5 b7 T! y4 y8 M, L! y& H END
7 Y% q/ Y# [( 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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