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Difficulties Using Solver for Staff Schedule - Complicated Criteria Set

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    Difficulties Using Solver for Staff Schedule - Complicated Criteria Set

    Hi, I have a similar problem and tried to use opensolver but ran into issues. maybe the problem is too complicated for excel.

    I'm trying to create a staff schedule where:
    24/7 department
    12 hour shifts (day and night)
    max 3 consecutive nights
    max 4 consecutive days
    3 skill types that are random among staff
    staff are Full time (6 shifts per 2 weeks minimum and soft maximum), part time (4 shifts per 2 weeks min and 6 max) or casual (6 shift/ 2 weeks max)
    in model i have 15 employees (actual will be 50-60ish)
    each shift has 1 person fill it for one day
    weekends and holidays may not require certain shifts
    each shift may require a specific skill
    eventually need special rules for specific staff like less nights or no nights.


    Approach:
    I create a table with repeating dates for the column and the 2nd column i have every shift repeating
    several other columns to show whether a shift is required for that date (if holiday or weekend)
    then the row headers had every staff
    body would be 1 or 0 to show the person taking the shift
    constraints would be on separate sheets that use combinations of index/match and sumproducts to count skills, or shifts and check if they fit a rule.
    objective is to have 1 shift filled by one person for every day (sum all of the different between actual and target) and aim for 0

    Outcome:
    Solver was supposed to fill in the table and comply with the constraints but it always goes crazy and tries to schedule a bunch of people in one row.



    Any help or direction would be greatly appreciated.
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    Last edited by AliGW; 07-03-2020 at 03:03 AM.

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    Re: Too many variable cells for Solver - Numbers that add up to a specific value

    Quote Originally Posted by icefire View Post
    Any help or direction would be greatly appreciated.
    Minimizing cell AC1, and adding a constraint so that AC1 >=0, the model can be solved locally (CBC engine).
    The setup requires a lot of time, but the solution is found almost immediatly.

    Not sure if this constraint is defined in the right range, though

    'Constraints(Days)'!$T$7:$W$7 >= 'Constraints(Days)'!$T$5

    HTH,

    Francesco
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    Re: Numbers to Add Up to a Specific Value

    Administrative Note:

    Welcome to the forum.

    We are happy to help, however whilst you feel your request is similar to this thread, experience has shown that things soon get confusing when answers refer to particular cells/ranges/sheets which are unique to your post and not relevant to the original.

    Please see Forum Rule #4 about hijacking and start a new thread for your query.

    As you are new, I have moved your hijack and the response received to this new thread.
    Ali


    Enthusiastic self-taught user of MS Excel who's always learning!

    Forum Rules (updated September 2018): please read them here.
    How to use the Power Query code you've been given: help here. More about the Power suite here.
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    Re: Too many variable cells for Solver - Numbers that add up to a specific value

    Quote Originally Posted by Hydraulics View Post
    The setup requires a lot of time, but the solution is found almost immediatly.
    "A lot" means 15 minutes, more or less.

    However, you would pay that price even if you were using an online server.

    HTH,

    Francesco

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    Re: Numbers to Add Up to a Specific Value

    Quote Originally Posted by AliGW View Post
    Administrative Note:

    Welcome to the forum.

    We are happy to help, however whilst you feel your request is similar to this thread, experience has shown that things soon get confusing when answers refer to particular cells/ranges/sheets which are unique to your post and not relevant to the original.



    As you are new, I have moved your hijack and the response received to this new thread.
    Sorry about that. Sure sign of a newb.

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    Re: Too many variable cells for Solver - Numbers that add up to a specific value

    Thank you very much. not sure what is going on but playing around with it some more seems to get some decent results.

    now to pile on more constraints and requirements
    Last edited by icefire; 07-04-2020 at 01:05 AM.

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    Re: Too many variable cells for Solver - Numbers that add up to a specific value

    I also encountered this "setup took a lot of time" problem. Please see the reply from Open Solver auther:

    We have to re-calculate the spreadsheet once for every decision cell (after changing that decision cell by +1) to extract the model from the spreadsheet for CBC. This can be slow, and is made worse as VBA can slow down over time for reasons (to do with memory?) we donít understand. Excel seems to use just one core when doing these re-calculations; it is not something we can influence. You can speed this up by making sure the workbook contains only the model spreadsheet, with no graphs or other calculations. SolverStudio with PuLP and an open source solver will be much faster as no spreadsheet recalculations are required. Hope this helps. Andrew
    Last edited by AliGW; 08-06-2020 at 02:18 AM. Reason: Please don't quote unnecessarily!

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    Re: Difficulties Using Solver for Staff Schedule - Complicated Criteria Set

    So I plugged in a full version with all the variables and it took 3 days to run. In the end, I didn't update the variables properly and decided not to try again given how long it took. I've been going down a rabbit hole ever since exploring Studio solver, programming with Julia, considered learning python or R or even Java since there is an existing package called OptaWeb for scheduling that requires modification to suit my needs. Optaweb is the most polished but Julia and StudioSolver seem the easiest to learn. I've been majorly slacking given the number of constraints I need to build but am slowly working away at this route.

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    Re: Difficulties Using Solver for Staff Schedule - Complicated Criteria Set

    Quote Originally Posted by icefire View Post
    I've been going down a rabbit hole ever since exploring Studio solver, programming with Julia, considered learning python or R or even Java since there is an existing package called OptaWeb for scheduling that requires modification to suit my needs.
    If you are willing to invest some time in learning Python, Pyomo or mip-python are 2 packages that you should test. The syntax follows the lines of a mathematical programming language, therefore it may be somewhat hard to grasp at the start, but there are many examples to be found online for both packages.

    An added bonus is the possibility to use a commercial solver (Gurobi, CPLEX), if you ever have the chance to put your hands on one of them.

    In a warehouse location problem I have recently built (100k variables, 13k constraints), OpenSolver needed more or less 4 hours to build the model, the Python version was below 1 minute.

    Finally, scheduling problems are often coded using constraint programming. If you haven't yet tried them, have a look at OR-Tools, and maybe miniZinc.

    HTH,

    Francesco

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