Experts:

I am developing a production scheduling application using Docplex CP and Python and have encountered an issue when using sequence variables

I have distilled the problem in an attempt to isolate the issue as follows.

I have a 2 stage production process as illustrated. Imagine it as a mixing process A followed by a bottling process B

Both A and B have sequence variables with transition matrices. For A there are multiple colours, and for B there are multiple bottle sizes. Consider the intervening object a tank. There is a temporal constraint that states that activities on B must start_after A.

THIS WORKS EXACTLY AS REQUIRED !!!

The problem arises if there are alternatives at B, as below:

If there is no sequence_var & transitions on A, it works fine, and sequences and transitions are respected and makespan is minimised per objective.

BUT, when there are sequence variables on all three resources, the result is NO SOLUTION. The solver runs endlessly until solve time limit without finding a solution.

NOTE: it is not infeasible

I figure this means that at least one variable is not instantiated.


Questions:
1. Is there an issue with sequence_var's in DOCPLEX CP?

2. How can I find which variable(s) are not instantiated during the solve?
3. What additional constraints should I add to properly constrain the problem?

Thanks

Ross

Experts:

I am developing a production scheduling application using Docplex CP and Python and have encountered an issue when using sequence variables

I have distilled the problem in an attempt to isolate the issue as follows.

I have a 2 stage production process as illustrated. Imagine it as a mixing process A followed by a bottling process B

Both A and B have sequence variables with transition matrices. For A there are multiple colours, and for B there are multiple bottle sizes. Consider the intervening object a tank. There is a temporal constraint that states that activities on B must start_after A.

THIS WORKS EXACTLY AS REQUIRED !!!

The problem arises if there are alternatives at B, as below:

If there is no sequence_var & transitions on A, it works fine, and sequences and transitions are respected and makespan is minimised per objective.

BUT, when there are sequence variables on all three resources, the result is NO SOLUTION. The solver runs endlessly until solve time limit without finding a solution.

NOTE: it is not infeasible

I figure this means that at least one variable is not instantiated.


Questions:
1. Is there an issue with sequence_var's in DOCPLEX CP?

2. How can I find which variable(s) are not instantiated during the solve?
3. What additional constraints should I add to properly constrain the problem?

Thanks

Ross

Experts:

I am developing a production scheduling application using Docplex CP and Python and have encountered an issue when using sequence variables

I have distilled the problem in an attempt to isolate the issue as follows.

I have a 2 stage production process as illustrated. Imagine it as a mixing process A followed by a bottling process B

Both A and B have sequence variables with transition matrices. For A there are multiple colours, and for B there are multiple bottle sizes. Consider the intervening object a tank. There is a temporal constraint that states that activities on B must start_after A.

THIS WORKS EXACTLY AS REQUIRED !!!

The problem arises if there are alternatives at B, as below:

If there is no sequence_var & transitions on A, it works fine, and sequences and transitions are respected and makespan is minimised per objective.

BUT, when there are sequence variables on all three resources, the result is NO SOLUTION. The solver runs endlessly until solve time limit without finding a solution.

NOTE: it is not infeasible

I figure this means that at least one variable is not instantiated.


Questions:
1. Is there an issue with sequence_var's in DOCPLEX CP?

2. How can I find which variable(s) are not instantiated during the solve?
3. What additional constraints should I add to properly constrain the problem?

Thanks

Ross

Experts:

I am developing a production scheduling application using Docplex CP and Python and have encountered an issue when using sequence variables

I have distilled the problem in an attempt to isolate the issue as follows.

I have a 2 stage production process as illustrated. Imagine it as a mixing process A followed by a bottling process B

Both A and B have sequence variables with transition matrices. For A there are multiple colours, and for B there are multiple bottle sizes. Consider the intervening object a tank. There is a temporal constraint that states that activities on B must start_after A.

THIS WORKS EXACTLY AS REQUIRED !!!

The problem arises if there are alternatives at B, as below:

If there is no sequence_var & transitions on A, it works fine, and sequences and transitions are respected and makespan is minimised per objective.

BUT, when there are sequence variables on all three resources, the result is NO SOLUTION. The solver runs endlessly until solve time limit without finding a solution.

NOTE: it is not infeasible

I figure this means that at least one variable is not instantiated.


Questions:
1. Is there an issue with sequence_var's in DOCPLEX CP?

2. How can I find which variable(s) are not instantiated during the solve?
3. What additional constraints should I add to properly constrain the problem?

Thanks

Ross