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  • GAMS mode goodies: Looking up the identifier part of a parameter, variable or set

    One of the nice features of Gams-Mode for Emacs is the possibility to quickly look up the identifier part of a variable, parameter or set. This is a nice feature in big models or when you haven’t worked with the model for some time. Just put the cursor somewhere on the parameter in the code you are looking at and hit F7. The screen will split and an additional side pane will appear.
    Here is an example: in the lower pane you see the file readdata.gms, where I am working on, and the cursor is on the parameter “total” (red
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  • Emacs and Stata

    Although I am not a great fan of multi-tasking I often use a lot of programs simultaneously for one task: For example, when I am writing a report in Word or with Emacs, I take notes in Emacs, search the internet and have my model results in the gdx-viewer.  Additionally my mail client is somewhere in the background and nowadays I have a messenger program open to talk to my collaborators. I don”t like this jumping from one program to another, but it is often necessary. This is also one of the reasons I switched to Emacs, because I can
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  • Golden Rule 2: Comments and Descriptions

    The next golden rule might also be obvious:Always add comments to your work and label your sets, variables, parameters and equations
    Now this might be obvious if you have a lot of time, but usually the rule is forgotten if you are stressed and want to finish what you are working on. Not writing comments will probably cost you a lot of time, if you take your model a year from now and see your code: Wow, that looks interesting and very ingenious, but what the %*?!  did I do here? If you send your model to somebody else for
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  • Golden Rule 1: Display and use your intuition

    The first golden rule for modeling is: Always display the results of your calculations and check them with your expectations about the results.
    Often you are working on a model doing a lot of preparing calculations (calibrating the model, preparing the data). Those calculations might be easy, for example calculating the shares for some parameter, but if you make an unnoticed error can cost you a lot of time and frustration.
    Here is a simple example. I want to calculate the shares for the investment function
     
     
    Calculating the share is not difficult thing, but you can make small
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  • How to update Gams and keeping an older version

    Gams is often updated and sometimes it can be good to have the old version still around (especially if you are not sure if the new version is working properly or if you are trying the beta version and want to switch back to the old version).
    What I usually do is the following:
    1. I rename the directory of my installed version to GamsOld
    2. Install the new version (directory “Gams”)
    3. That is almost all.

    The advantages ares:

    1. first of all, I still have the older version around (I usually keep one older version and delete the others).
    2. As I work
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