standardize decision variables in `locate`

[jGaboardi]

Currently, we have a mishmash of decision variable notation within the locate models that are based on the original models' formulations, adaptation of such, or something. We should standardize them for one unified set.

• $X =$ demand/client locations
• $Y =$ service/facility locations

xref #295

[jGaboardi]

@gegen07 @ljwolf

Do either of you have any strong opinions about this?

[gegen07]

I'm fine with it. Should we assign the names in the builder process instead of passing the name as an argument?

[jGaboardi]

Should we assign the names in the builder process instead of passing the name as an argument?

This is a good point... I was halfway thinking we should keep the variable names as default keyword values, but then I realized that we don't even allow users to pass in different names now.

Can we think any of reason not to move the variable names to within the builder methods, like you suggest?

In terms of action plan, we need to figure out if #295 is still a problem.

Also, we will need to update:

• docstrings
  • check formulations
  • check language in Parameters and Returns sections, etc,
• notebooks
  • check formulations
  • check naming of decision variable labels