In April 2011, Mdsuhair asked a question at the Chandoo.org Forums
This is a candidate for Solver.
This post will walk us through the solution to the problem using Solver. It uses Solver and screen shots from Excel 2007.
All versions of Excel have solver available. Users should note that the screen shots may not match your version although the functionality will, some of the functions appear in different locations in different versions of Solver.
What and Where Is Solver
What is Solver
Solver is an Excel add-in that can solve problems by enabling a Target cell to achieve some goal.
This goal may be to minimse, maximise, or achieve some target value.
It solves the problem by adjusting a number of input cells according to a set of criteria or constraints which are defined by the user.
Where is Solver
Solver is an Excel add-in supplied with Excel, but not enabled by default.
To enable solver
File, Excel Options, Add-ins, Manage Excel Add-ins, Select the Solver Add-in checkbox
Solver will now appear as a New Tab on the Data, Analysis Tab
Solver Example
This post is based around a worked example Solver Example File, the file is compatible with all versions of Excel.
Defining the Problem
Mdsuhair had a series of 8 Items each which had a value:
He wants to know which items should be combined so that the sum of the values of the items is nearly equal.
To do this we need to assign each item into a Bucket. Namely Bucket A and Bucket B.
We will put values of 1 into a Bucket for each Item to show that it is assigned to that Bucket and a value of 0 to show that the bucket is empty (In/Out) Value.
We can start by adding a Total Column, which counts items in Buckets A + Bucket B for each Item, It then totals the totals.
We also know that we need to work out the Value of each Item in each Bucket
We do this by multiplying the Items Value by the Buckets (In/Out) value
Finally we need to add up the values in each Bucket and work out the difference between them
Mdsuhair’s original problem was to minimise the difference between the sum of the values in the 2 buckets.
Now we can place values of 1 in the buckets manually and Excel will show us the value of each Bucket and the Difference between them in Cell G11.
I have applied some conditional formatting to show when a cell has a value > 0.
The problem is that there are 28 or 256 combinations of answers, and to test them all manually at 1 every 5 seconds would take 21.3 minutes, assuming we can keep up that pace and remember which was the best combination.
This is where solver comes to the fore.
Applying Solver
To apply solver we need to define a series of requirements, rules and constraints.
These requirements, rules and constraints guide solver and set limits which allow solver to quickly narrow in on the answer.
What are our rules
Our main requirement is to minimise the difference between the value of the 2 buckets.
The difference between the 2 buckets in our example is cell G11, the sum of Bucket 2 values minus the Sum of Bucket 1 values.
We want to have G11 as low as possible but greater than or equal to 0.
We also know that an item can only be in Bucket A or Bucket B, it can’t be in both and can’t be Broken apart.
That is 2 Constraints for each Item
Firstly The Total column must be equal to 1
Secondly the Buckets Values must be Integers
We also know that the Total Number of Items is 8, this is another constraint.
We will discuss how these constraints are used in the next section
The Solver Window
This section will explain the solver window and its use in defining the problem within solver.
A Blank Solver Window
A Filled Solver Window
Set Target Cell:
This is the Target cell which is the cell which you are trying to solve the problem for.
Our Target cell is G11, The difference between the 2 Buckets values
Equal To:
The Equal To: section defines what we want to do with our Target Cell.
We want to achieve the same value in each Bucket and so the difference between the Buckets will be 0.
It might sound strange but we don’t want to minimise that difference. A minimal value will be achieved when all the Items are placed in Bucket A, as our equation for G11 will then have 0 – Total which is –Total, which is more minimal than 0.
Another way to constrain this is to Change G11 to =Abs(G10-H10)
This allows us to use Min as an Equal To: Value
But for now we can just leave G11 as =G10-H10 and we will set the Equal To: section as 0.
By Changing Cells:
Changing Cells: refers to the cells which will be modified by Solver to try and solve the problem.
We want to let Solver change the number of items in each bucket, this is the range: $C$2:$D$9
Hint: You can try the Guess button next to the Range Reference and Solver will take a Guess at what cells the problem is dependent on.
Always check this if you use it, especially in complex models.
Subject to the Constraints:
Constraints are the rules which define the limits of the possible solutions to the problem
We will add several constraints for our rules:
1. The Total column must be equal to 1 for each Item
2. The Bucket Value must be an Integer
3. The total contents of the 2 buckets must be 8 items
4. You could add a further constraint that each Bucket should hold the same number of items
Hint: As a general Rule, Under Constrain rather than over constrain! You can always add more constraints later.
To do this we will use the Add Constraint Button
1. We need to add a constraint for each cell in the Range E2:E9 that it is only allowed to be = 1
This constraint must be applied for each cell in the range E2:E9
2. We need to add a constraint for each cell in the Range C2:D9 that it is only allowed to be an integer
This constraint must be applied for each cell in the range C2:D9
3. We need to add a constraint for the Total of the 2 Buckets, E10=8
You can Change or Delete Constraints if you make a mistake by selecting the appropriate constraint and using the Change or Delete Buttons
Save and Load Solves Parameters
Selecting the Options Button there is the Option to Save Model and Load Models.
Hint: The Save/Load Models has been shifted onto the main Solver dialog in Excel 2010.
Using the Save Model and Load Model options you can Save and the Load the Solver Parameters for your model. The Save Model saves the parameters in a Range of cells as shown below.
This allows an easy way to actually setup and/or change the solver parameters.
Hint: Setup one constraint using solver then Save the model. Edit the model on the worksheet and re-load the model as required.
Note: That the parameters although when saved show as True/False or Numbers are all Excel Equations, see above.
This means you can edit them to change the Constraints and Parameters as required and re-load them into solver.
I have included 3 sets of Parameters for our model.
These are:
- Base Case – Forces bucket values to be equal, Allows uneven bucket counts
- Equal Sized Buckets – Forces each bucket to contain the same number of items
- Force an error – Which forces an error in the solver model
Load each model and try them at your leisure.
Running the Solver Model
Warning: Solver is a computationally complex add-in, so once your model is setup, Save your Workbook.
Prior to running the model there are a few parameters we should look at to ensure the model solves correctly.
On the main Solver window select the Options button. (Some of these parameters are on the Main Solver window in Solver 2010)
Generally you can accept the defaults but in this case we will change the following
Assume Linear Model – Select
Assume Non-Negative – Select
Note: Solver in Excel 2010 will return a better answer without these 2 parameters enabled by default
The other 2 parameters which you may need to change from time to time is
Precision: Precision is a number from 0 to 1 and higher means more precise
Tolerance: Tolerance shows how far away from a Number, an Integer constraint is allowed to be
The use of the Estimates, Derivatives and Search parameters are beyond the scope of this post. I direct you to the Excel Help on these subjects, by selecting the Help button.
Run the Model
To Run the Model, select the Solve Button from the main Solver menu.
The main status bar in Excel will flash up a number of statistics about the internal workings of the Solver add-in. Generally these flash by and are too fast to read. If a model is too complex it may stall and you won’t see any movement for a while. Solver generally recovers from these problems itself.
Once the Solver model finishes it will display a dialog of the results and allow you to do several things
First thing to note is that “Solver Found a Solution“.
If it has found a solution, the worksheet cells will be changed to show the solution
You now have 4 options:
- Run a Report
- Save a Scenario
- Return to the model
- Check Your Results
Run a Report
Run a report by clicking the report you want.
A new sheet will be added to your workbook depending on the report but will be called:
- Answer Report 1,
- Sensitivity Report 1
- Limits Reports 1
etc.
Note, that not all reports are relevant at all times, depending on the Constraints you have applied.
Save a Scenario
Selecting the Save a Scenario button takes you to the Save Scenario dialog.
Type in a Name and the Scenario of your model is saved as a Scenario.
Scenarios as available for use in the Scenario Manager, which is accessed from the Data, What-If-Analysis Tab
Return to the model
You can return to your model and either:
- Keep Solver Solution
- Restore Original Values
Check the Results
Solver is probably the most Black Box’ish of systems within Excel. As such any results it puts out must be manually checked for suitableness before further use.
These checks for realness, should as a start confirm that the results meet all the criteria supplied.
Are the results roughly what were expected?
Are any Minimums or Maximums violated?
What If Solver Doesn’t Find a Solution?
From time to time Solver will return with an error that a “Solver could not find a feasible solution.”
When this happens it is indicating one of several possibilities:
- Your model is over or under constrained
- Your model constraints are impossible to meet
- Your model constraints have an error
Start by checking the current constraints for errors and ambiguities
Eg: in our case we have 8 items so requiring the Count of the two buckets to be 20 is impossible to meet
My Solver Answer has Strange Numbers?
In solver up to and including Excel 2007, solver would commonly return numbers like 3.5E-18.
This is 0.0000000000000000035, which is effectively 0
If your model returns these, feel free to go through the model and change them to 0, in our model we should also check as the corresponding 1, may in fact be 0.9999999999999999965.
It should be noted that this problem in Solver in Excel 2010 does not occur as often but will still occur.
What and How have you used solver in the past?
What and How have you used solver in the past?
Let us know in the comments below:
25 Responses to “Shift Calendar Template – FREE Download”
Hi Chandoo,
your recent postings include only Excel 2007 templates. Unfortunately the company I work at still runs Excel 2003. Is it possible to get your awesome files in other excel version as well?
Thanks so much for your great excel stuff!
Is it possible to do this for shifts with hours instead of days? To organise a three shift day?
Thanks in advance,
Stelios
In my organization there are 45 employees i need split then into three shifts ex:A shift:14,B shift:14,C shift:14 and week off:3 kindly help me on this.
@Masthan
You need to understand what rules your company has for the various shifts / roster combinations
Chandoo, I once did a shift control spreadsheet for my team. I put one person in each line, the columns were the days. I put a shift code in each cell indicating in which shift that person should work, or if the person were out that day. I have two codes for being out. One is for vacations and one is to compensate days worked in weekends. This way I was able to count how many persons I have in each shift, how many were on vacations and how many were out compensating (that's the term we use here) weekend worked hours.
Later I included the possibility of a person be in two lines one for normal hours other for overtime. This is mainly used for planning purposes. If you would like I can send you an example. The only problem of this spreadsheet is that we don't have a person view, only this consolidated view.
Hi George, I would like to have a copy of your spreadsheet if you can share it.
Thanks in advance, Chuck
Hi Chandoo,
Where is the code located ? is it VBA ? If so , how do you hide it ? Or it is .NET ?
Thx
@Idan
.
No VBA or code, it is all done with Mirrors.
Only Joking,
.
But there is no VBA or code,
It is all done with Named Formulas and Lookups.
Have alook at the cells in the calander area and Named Formulas in the Formulas, Name Manager Tab.
How can i calculate between two or more different workbooks? Please, reply me as early as possible.
@Anand
Open the workbooks you want to link to
Start a formula = and click and change between workbooks as required.
You can use the View, Switch window menu to change workbooks mid formula
The format for using workbooks is
=[Workbook.xlsm]Sheet1!$A$1
or
=SUM('[Book2.xls]Sheet1'!$A$1:$D$10)
etc
Hi Chandoo,
I am working with a call centre wherein i ned to update at the month end 20 to 30 employees login hours which are defict to track it at the month end is very difficult is there any template which can be made to track that why on a particular day a guy who needs to be on calls was why not on calls.
Thank you so much Chandoo. This is really helping me. As usual, you rock.
What's FortyTwoDays and Calendar in Name manager?
Both are unused and FortyTwoDays doesn't make any sense.
I have a SQL db that contains records of events scheduled/completed on a particular date. Can this method ous building a calendar be used to display those events on the respective day?
Positively awesome!
I'm attempting to help a friend create a schedule for adult classes - and of course its not"paid help". Here is the scenario:
20 classes, instructor, room#, student class size, start date, number of class days (need to subtract weekends)
class
instructor
room
students
start
#days
PATH
karen
201
21
01/01/13
11
BILLING
jane
401
15
01/12/13
13
MEDISOFT
mike
301
11
01/25/13
9
he'd like to see these classes show up in different colors within the same month's calendar chart. He can draw it, but I'd like to see it done automatically through data, and I just can't visualize it, but I KNOW this will work - can you help?
Jan 🙂
Dear chandoo,
Try many way to download still can't access. Any way we want to try out 3 shifts with 3 guys in a group .eg Group A Morn, Group B Night and Group C Rest. And every each group must work on sunday to take turns. In fact we are security teams so that's why sunday is required to work. Pls guide and show how to put in the working calendar. Thank you in advance.
I've been trying to copy and/or recreate this to use in a workbook I'm doing for the transportation department I'm working for. I need to have the calendar on the first sheet in my document (it has graph's from data on another sheet). I'm trying to use it to track (with the conditional formatting) accidents and injuries. I've redone the conditional formatting to do 4 different accident types (no injury, near miss, OSHA recordable injury and work loss injury), but when I enter the formula's you have in the calendar portion where it says "DateOfFirst-FirstWeekDay" I can't figure out how you did that. Are you able to help?
I would like to use Excel to solve the following problem for a community work. I want to create a Driver schedule for a given month from a pool of volunteers for a community service. Each of these volunteers can drive only on specific days in a week. I would like to populate the driving schedule for each weekday with primary, secondary and tertiary drivers in a random fashion so that I do not overburden one person. I would greatly any help you can provide.
Hi chandoo,
Thanks for your valuable effort for create this template and let me know how to add multiple employees in the the Roaster.
Hi Chandoo,
This article on shift roaster is very helpful. Could you please let me know how i can use the same for n number of resources who work 24/7, considering their leaves and holidays?
Thanks,
Savitha
Hi Chandoo,
This article on shift roaster is very helpful to all. Could you please let me know how i can use the same if I want to add for some more shifts, since the color is not getting change if I add more shifts like 4,5 etc.,
Thanks,
Murali
nice post
How can I change the date to 2017 under Shift Data worksheet.
solution 1:
mydata=B2:C16
stoplist=E2:E8
=LET(RNG,A2:A16,SMR,C2:C16, F,(RNG=E2)+(RNG=E3)+(RNG=E4)+(RNG=E5)+(RNG=E6)+(RNG=E7)+(RNG=E8),SUM(SMR)-SUM(SMR*F))
=LET(RNG,A2:A16,SMR,C2:C16,RH,N(B2:B16=B2), F,(RNG=E2)+(RNG=E3)+(RNG=E4)+(RNG=E5)+(RNG=E6)+(RNG=E7)+(RNG=E8),TOT,SUM(SMR)-SUM(SMR*RH*F),SUM(SMR*RH)-SUM(SMR* RH*F))
ALTERNATE SOLUTION
=SUM(C2:C16)-SUM(FILTER(C2:C16,ISNUMBER(BYROW(A2:A16,LAMBDA(a,TOROW(SEARCH(a,E2:E8),2))))))
=SUM((B2:B16=B2)*(C2:C16))-SUM((ISNUMBER(BYROW(A2:A16,LAMBDA(a,TOROW(SEARCH(a,E2:E8),2))))*(B2:B16=B2)*(C2:C16)))
let
Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
#"Replaced Value" = Table.ReplaceValue(Source,null,";",Replacer.ReplaceValue,{"Column1"}),
#"Transposed Table" = Table.Transpose(#"Replaced Value"),
#"Removed Other Columns" = Table.SelectColumns(#"Transposed Table",{"Column1", "Column2", "Column3", "Column4", "Column5", "Column6", "Column7", "Column8", "Column9", "Column10", "Column11", "Column12", "Column13", "Column14", "Column15", "Column16", "Column17", "Column18", "Column19", "Column20", "Column21", "Column22", "Column23", "Column24", "Column25", "Column26", "Column27", "Column28", "Column29", "Column30", "Column31", "Column32", "Column33", "Column34", "Column35", "Column36", "Column37", "Column38", "Column39", "Column40", "Column41", "Column42", "Column43", "Column44", "Column45", "Column46", "Column47", "Column48", "Column49", "Column50", "Column51", "Column52", "Column53", "Column54", "Column55", "Column56", "Column57", "Column58", "Column59", "Column60", "Column61", "Column62", "Column63", "Column64", "Column65", "Column66", "Column67", "Column68", "Column69", "Column70", "Column71", "Column72", "Column73", "Column74", "Column75", "Column76", "Column77", "Column78", "Column79", "Column80", "Column81", "Column82", "Column83", "Column84", "Column85", "Column86", "Column87"}),
#"Merged Columns" = Table.CombineColumns(#"Removed Other Columns",{"Column1", "Column2", "Column3", "Column4", "Column5", "Column6", "Column7", "Column8", "Column9", "Column10", "Column11", "Column12", "Column13", "Column14", "Column15", "Column16", "Column17", "Column18", "Column19", "Column20", "Column21", "Column22", "Column23", "Column24", "Column25", "Column26", "Column27", "Column28", "Column29", "Column30", "Column31", "Column32", "Column33", "Column34", "Column35", "Column36", "Column37", "Column38", "Column39", "Column40", "Column41", "Column42", "Column43", "Column44", "Column45", "Column46", "Column47", "Column48", "Column49", "Column50", "Column51", "Column52", "Column53", "Column54", "Column55", "Column56", "Column57", "Column58", "Column59", "Column60", "Column61", "Column62", "Column63", "Column64", "Column65", "Column66", "Column67", "Column68", "Column69", "Column70", "Column71", "Column72", "Column73", "Column74", "Column75", "Column76", "Column77", "Column78", "Column79", "Column80", "Column81", "Column82", "Column83", "Column84", "Column85", "Column86", "Column87"},Combiner.CombineTextByDelimiter("|", QuoteStyle.None),"Merged"),
#"Split Column by Delimiter" = Table.ExpandListColumn(Table.TransformColumns(#"Merged Columns", {{"Merged", Splitter.SplitTextByDelimiter(";", QuoteStyle.Csv), let itemType = (type nullable text) meta [Serialized.Text = true] in type {itemType}}}), "Merged"),
#"Added Prefix" = Table.TransformColumns(#"Split Column by Delimiter", {{"Merged", each "|" & _, type text}}),
#"Replaced Value1" = Table.ReplaceValue(#"Added Prefix","||","|",Replacer.ReplaceText,{"Merged"}),
#"Split Column by Delimiter1" = Table.SplitColumn(#"Replaced Value1", "Merged", Splitter.SplitTextByDelimiter("|", QuoteStyle.Csv), {"Merged.1", "Merged.2", "Merged.3", "Merged.4", "Merged.5", "Merged.6", "Merged.7", "Merged.8"}),
#"Removed Columns" = Table.RemoveColumns(#"Split Column by Delimiter1",{"Merged.1"}),
#"Removed Duplicates" = Table.Distinct(#"Removed Columns")
in
#"Removed Duplicates"