Originally posted by: Valentin_J

Hello everyone,

I would like to know how is it possible to erase some parameters of a decision variable.

I mean, I have a dvar x which represent travel between nodes, and I know that some are impossible so I want them to not be include in the process so it may be faster.

Thank in advance, have a nice day.

Hi

I encourage you to have a look at exploiting sparsity in https://www.ibm.com/support/knowledgecenter/SSSA5P_12.10.0/ilog.odms.ide.help/OPL_Studio/opllanguser/topics/opl_languser_modelingtips_sparsity_better.html

regards

Originally posted by: Valentin_J

First of all thank you,

to be honest i didn't get the whole code from your topic, is that it that doing the restriction ?

{connection} CPs[p in Products] = { c | <p,c> in Routes };
assert forall(p in Products) 
   sum(o in Orig[p]) Supply[<p,o>] == sum(d in Dest[p]) Demand[<p,d>];

Regards

Hi,

so suppose you have 3 nodes A,B,C and you want to know how much to move between A and B and then B to C.

You could use an array

dvar int move[nodes][nodes];

but this array is 3*3 and you will only use 2 decision variables.

So what is smarter is to use only arcs.

And then you ll have 2 decision variables, one per arc

You got the idea ?

regards

Originally posted by: Valentin_J

In fact,

To know how much to move, I already have a cost matrix, and my x[N][N][K] (where N is the number of nodes and K my et of vehicles) is a boolean. I want to set at 0 some of edge of x 

like :

forall (k in K)

     x[i][j][k]=0;

Where I will be able to decide which couple i,j I want to disable. Unfortenately it's obviously not working like that.

So in my objective function they won't appear because they are equal to 0.

minimize
  sum(k in K, i in N, j in N)
    c[k][i][j]*x[i][j][k];

Sorry if my answer misses the point here.

Regards.

Hi,

of so you could eitherkeep your x which consumes some memory for x or do something a bit smarter:

You use a tuple set with i,j,k so that x of i,j,k is not 0

And then instead of

x[K][N][N]

you will use

x[S]

which is smaller and does not containe all the 0 you got rid of

regards

https://www.linkedin.com/pulse/low-barrier-entry-optimization-through-cplex-alex-fleischer/

Originally posted by: Valentin_J

Ok, so I may first create the global set and then substract what I want to disable ?

I know how to define a set but not how to substract them 

tuple S {
  int k;
  int i;
  int j;
}

{S} s = {<i,j,k> | i in N, j in N, k in K};

Then another question all my constraint will work fine just if I update x[S] ?

from :

    forall (i in P)    sum(k in K)sum(j in N) x[i][j][k]==1;

to :

    forall (i in P)    sum(k in K)sum(j in N) x[S]==1;

Best regards.

Hi,

1)

You may use diff : https://www.ibm.com/support/knowledgecenter/SSSA5P_12.5.0/ilog.odms.ide.help/OPL_Studio/opllang_quickref/topics/tlr_opl_diff.html

2)

forall (i in P)    sum(k in K)sum(j in N) x[<i,j,k>]==1;

regards

Originally posted by: Valentin_J

Thank again !

Ok I manage to do my set without links I wanted to disable.

Unfortunately as expected, all my constraints are now out of index because I erased some of arcs.

Am I forced to change bounds for all my constraints ?

Regards.

Hi,

now is the time to move from

forall (i in P)    sum(k in K)sum(j in N) x[<i,j,k>]==1;

to

forall (i in P)    sum(k in K)sum(j in N:<i,j,k> in S) x[<i,j,k>]==1;

regards

Originally posted by: Valentin_J

hi,

Verry sorry to bother you as much.

but it says me that the operator is not available :

Opérateur non disponible pour <int,int,int> IN tuple<k:int,i:int,j:int>

To be honest I don't really get the point.. 

You are trying to cut S from sums ? Just include all x that are in S ?

Moreover, just to be sure, I want the intervale s. Am I right writing ?

tuple S {
  int k;
  int i;
  int j;
}

{S} s0 = {<i,j,k> | i in N, j in N, k in K};

{S} s1 ={<0,j,k> | j in D, k in K};
{S} s2 ={<i,0,k> | i in N, k in K};
{S} s3 ={<i,2*n+1,k> | i in P, k in K};
{S} s4 ={<i,i,k> | i in N, k in K};

{S} s = s0 diff s1 diff s2 diff s3 diff s4;

Hi

range N=1..4;
range K=1..3;
range D=1..2;
range P=2..3;
int n=1;

    tuple S {
      int k;
      int i;
      int j;
    }

    {S} s0 = {<i,j,k> | i in N, j in N, k in K};

    {S} s1 ={<0,j,k> | j in D, k in K};
    {S} s2 ={<i,0,k> | i in N, k in K};
    {S} s3 ={<i,2*n+1,k> | i in P, k in K};
    {S} s4 ={<i,i,k> | i in N, k in K};

    {S} s = s0 diff s1 diff s2 diff s3 diff s4;
    
    execute
    {
      writeln(s);
    }

works fine

If it s too difficult you may start with a first model that does not exploit sparsity.

And you may have a look at getting started https://www.ibm.com/support/knowledgecenter/SSSA5P_12.8.0/ilog.odms.studio.help/pdf/gsoplide.pdf

regards

Originally posted by: Valentin_J

Hi, 

I manage to solve my issue and all my constraints thank to you !

And I better understand tuples and sets now.

have a nice day, best regards.

Originally posted by: Valentin_J

hi again !

I have got one more question about these tuples, how can i conditioning them ?

like :

{S} s7 ={<i,j,k> | if (t[i][j]+d[j]+t[j][n+i]>L) i in P,j in N, k in K };

best regards.

Hi,

see https://www.ibm.com/developerworks/community/forums/html/topic?id=91c615e8-af72-44e1-94d1-2b680ca1b3b2&ps=25

in  https://www.linkedin.com/pulse/making-decision-optimization-simple-alex-fleischer/

which in your example could be

range N=1..4;
range K=1..3;
range D=1..2;
range P=2..3;
int n=1;
int L=3;
int t[i in 1..10][j in 1..10]=i+j;
int d[i in N]=i;

    tuple S {
      int k;
      int i;
      int j;
    }

    {S} s0 = {<i,j,k> | i in N, j in N, k in K};

    {S} s1 ={<0,j,k> | j in D, k in K};
    {S} s2 ={<i,0,k> | i in N, k in K};
    {S} s3 ={<i,2*n+1,k> | i in P, k in K};
    {S} s4 ={<i,i,k> | i in N, k in K};

    {S} s = s0 diff s1 diff s2 diff s3 diff s4;
    {S} s7 ={<i,j,k> | i in P,j in N, k in K : (t[i][j]+d[j]+t[j][n+i]>L) };
    
    
    execute
    {
      writeln(s);
      writeln(s7);
    }

regards