Optimization Tool Help - Subset Sum Problem

Question

Hi all,

I'm hoping someone here might be able to help with a problem we are currently facing with the Optimization tool in Alteryx Designer. We are trying to use the tool to find and flag which subset of transactions make up a specified target (which could be made up from an unknown number of transactions).

However, we are finding that the tool will often specify solutions which are incorrect. In the attached workflow, we are trying to find a specific total, and the tool has claimed to have found a solution which has a different value than the target.

I can see in the D output node that it is in fact trying to find our correct value, and put in a 'Slack' value of 0.13, which we cannot have. In my constraints I have specified using '==' which I would assume would have a slack of 0.

We are okay if the workflow cannot find a solution, but we cannot have these false positives where the target value is 'close enough' as we need exact matches.

Is it possible to manually adjust this Slack value (despite my constraint using ==)? Any ideas as to why this is happening?

Appreciate any insight on this as we are quite confused!

Thanks

Subset Sum Community Post.yxmd

OllieClarke · Answer

Hi @DanMorton

I couldn't find the cause of the issue, but these links might be useful:
https://github.com/alteryx/AlteryxPrescriptive/tree/master is the source code for the optimisation R tools. /R/solveModel.R seems to be the code used by the optimisation tool.

https://rdrr.io/github/alteryx/AlteryxPrescriptive/man/AlteryxSolve.html This is a more interactive (maybe) documentation of the packages.

Hope that helps,

Ollie

DanMorton · Answer

Thanks for taking a look at this one - we have included some checks to verify whether we can get exact matches or not, however that doesnt help us too much unfortunately, particularly if the tool flags a false positive before it finds a genuine solution to the problem.

Also we are typically trying to minimise the number of transactions to match the target.

We have also tried on multiple machines and recreated the same problem, so the issue is not fixed by just replacing the tool and setting up from scratch again.

Thanks,
Dan

BS_THE_ANALYST · Answer

@DanMorton I know it's not as satisfying but you could just include a check to see that the Slack value is in fact 0 by parsing it out with something like text to columns etc. If it's not 0, use a message tool to trigger an error. Effectively, it's providing the same result as the tool erroring itself.