VRP algorithm

[alessio88]

Hi, I'm using a VRP algorithm that gives me the perfect solution but it takes
too much time to solve problems with more than 12 nodes. I post them the
.mod and the .dat files

param n >= 0;
param K >= 0;
param C >= 0;
set N := 0..n;
set A := {i in N, j in N: i <> j};
param c{A} >= 0;
param d{1..n};
var x{A} binary;
var u{1..n} >= 0 ;
minimize costo: sum{i in N, j in N: i<>j} c[i,j]*x[i,j];
s.t. arcoentrante{j in 1..n}: sum{i in N: i <> j} x[i,j] = 1;
s.t. arcouscente{i in 1..n}:
sum{j in N: j <> i} x[i,j] = 1;
s.t. veicoli: sum{j in 1..n} x[0,j] <= K;
s.t. sottocicli{i in 1..n, j in 1..n: i <> j}: u[j] - u[i] + C*x[i,j] <= C -
d[i];
s.t. bound{i in 1..n}: d[i] <= u[i] <= C;


param n := 7;
param K := 10;
param C := 150;
param d := 1 50, 2 50, 3 50, 4 150, 5 50, 6 50, 7 50;
param c : 0 1 2 3 4 5 6 7:=
0 . 4.5 6.5 7.5 10 13 10 10
1 8.5 . 1.9 3 2.7 14 12 12
2 13 5 . 1.1 3.5 16 13 13
3 12 4.5 4.5 . 2.4 14 12 12
4 13 6.5 5 6 . 16 13 13
5 8.5 16 15 16 19 . 2.6 9
6 6 14 13 14 16 2.6 . 1
7 5.5 13 12 13 15 3.5 8 .;

Can you give me a heuristic model in AMPL mod file? Thank you very much
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[Iván Riera]

I have mine almost perfect...but still not working:

###Sets aNd parameters###
param N :=17;
param k :=3;
set dem_Nodes := {2..N};
set Nodes ordered := {1..N};
set veh := {1..k};
set Arcs := {i in Nodes, j in Nodes: i<>j};
param Q{veh}>0;
param q{Nodes}>=0;
param C{Arcs};


###Variables###
var x{Arcs, veh}, binary;
var y{Arcs}, binary;
#var z{Nodes}, integer;


###The objective fuNctioN###
minimize Total_cost:
sum {t in veh} sum {(i,j) in Arcs} C[i,j] * x[i,j,t];

###CoNstraints###
#Starting from depot (Node 1), a vehicle must visit a customer i.
subject to Start{j in dem_Nodes}:
sum{i in Nodes: i<>j} y[i,j]=1;


#After visiting a customer i,the vehicle must leave for aNother
customer j.
subject to CoNtinue{i in dem_Nodes}:
sum{(i,j) in Arcs: i<>j} y[i,j]=1;


#The Nº of vehicles going from Node 1 to all Nodes j must be equal to
k.
subject to Going:
sum{j in dem_Nodes, i in Nodes: i<>j} y[1,j]=k;


#The Nº of vehicles returNing to Node 1 from all Nodes i must be equal
to # k.

subject to Backing:
sum{i in dem_Nodes, j in Nodes: i<>j} y[i,1]=k;


#Each vehicle must carry less thaN or equal to its capacity.
subject to Capacity:
sum {t in veh} sum {i in dem_Nodes, j in Nodes: i<>j}
x[i,j,t]*q[j]<=Q[k];


#There must be a link betweeN xkij aNd yij variables. Each Node,
except


#the depot, caN oNly be served oNce by oNly oNe vehicle.
subject to Served:

sum{i in Nodes, j in Nodes: i<>j} x[i,j,1] + sum{i in
Nodes, j in
Nodes: i<>j} x[i,j,2] + sum{i in Nodes, j in Nodes: i<>j} x[i,j,3]
=sum{i in Nodes, j in
Nodes: i<>j} y[i,j];


#The solutioN must Not coNtain aNy cycle using the Nodes 2,3,..,N.
Not
#coNtain aNy subtours of these Nodes.

subject to Servedonly:
sum {t in veh} sum{i in Nodes, j in Nodes: i<>j} x[i,j,t]
= sum{i in Nodes, j in Nodes: i<>j} y[i,j];

If you see the fail and you can run it, please tell me!!

[alessio88]

Your model seems to be correct but you haven't written the data, solving it
AMPL gives:

Error executing "solve" command:
error processing objective Total_cost:
no value for C[1,2]

I use the student edition so if the variables or the constraits are more
than 300 the program doesn't work,
with N=17 I don't know if it could run.

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[adel ali]

Hi Alessio88
I hope you are doing fine.
Can you please explain for me the meaning of your abbreviations because I am
trying to code your code in Cplex .. Or if you have it ready on Cplex Could
you please send it to me as soon as you can because I am in urgent need for
it

I do appreciate your help and support
Regards
Adel

alessio88 wrote:
>
> Hi, I'm using a VRP algorithm that gives me the perfect solution but it

> takes too much time to solve problems with more than 12 nodes. These are

View this message in context: http://old.nabble.com/VRP-algorithm-tp33850933p35088860.html

[nockma...@gmail.com]

Cplex model languages for VRP algorithm

Excuse me, could you please help me to change the this example from AMPL version to Cplex version??

Thank you very much.

เมื่อ วันอังคารที่ 22 พฤษภาคม ค.ศ. 2012 1 นาฬิกา 15 นาที 36 วินาที UTC+7, alessio88 เขียนว่า:

[Robert Fourer]

We can help with solving your AMPL model, using CPLEX for AMPL, but; we are not prepared to offer help for other CPLEX software. You might be able to get more CPLEX help from IBM; try searching on "ibm cplex forums" for links to some websites that provide answers to user questions.

Bob Fourer
am...@googlegroups.com

=======

[มณีรัตน์ การรักษ์]

Thanks you for your help me.

เมื่อ 29 มี.ค. 2016 21:09 "Robert Fourer" <4...@ampl.com> เขียนว่า:

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[Robert Fourer]

AMPL only describes models; it does not describe heuristic algorithms for solving. However a simple approach to using AMPL in a heuristic way is to set a time limit for the solver; then the solver will return the best solution it has found so far. or a problem with binary variables, this may even be the optimal solution, though you won't have a proof of optimality since the solver stopped at the time limit.

Each solver has its own options for setting a time limit, so you'll have to look them up on the appropriate solver page -- see http://ampl.com/products/solvers/.

Bob Fourer
am...@googlegroups.com

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Sent: Tuesday, April 18, 2017 3:35 PM
To: AMPL Modeling Language