Clustering problem constraint error CPLEX cannot extract expression

Question

I've written following code for a clustering problem:

range N=1..10; 
range M=1..2; 
float distance[N,N]=...;
dvar boolean x[M,N]; 
dvar float+ Z; 

minimize Z;

 subject to {
   forall(i in N, j in N, k in M)
         distance[i,j]*x[i,k]+distance[i,j]*x[j,k]-Z<= distance[i,j];
  
   forall(j in N)
    sum(i in M)x[i,j]==1; }

I keep getting "CPLEX cannot extract expression" and "OPL cannot extract expression" errors. Am I writing the first constraint wrong?

Here's the mathematical model:model

Alex Fleischer · Accepted Answer · 2023-12-05 11:06:05Z

0

range N=1..10; 
range M=1..2; 
float distance[n1 in N,n2 in N]=abs(n2-n1);
dvar boolean x[N,M]; 
dvar float+ Z; 

minimize Z;

 subject to {
   forall(i in N, j in N, k in M)
         distance[i,j]*x[i,k]+distance[i,j]*x[j,k]-Z<= distance[i,j];
  
   forall(j in N)
    sum(i in M)x[j,i]==1; }

works fine

answered Dec 5, 2023 at 11:06

Alex Fleischer

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thanks! it works but I've laready set the distance matrix, it's a 10x10 matrix let's say, and it has 0's diagonally ofc. In my previous code I tried to retrieve distance array from .dat file, but it didn't work, am I missing something?
– Cmrs
Commented Dec 5, 2023 at 19:34
Then change float distance[n1 in N,n2 in N]=abs(n2-n1); into float distance[N,N]=...;
– Alex Fleischer
Commented Dec 6, 2023 at 10:31

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