Can't seem to get Constraint.Implies() working.

[s.vanho...@gmail.com]

As a student ICT & Software Engineering I am currently working on a prototype crop planning optimization with Optano modelling in .NET C# using the GLPK Solver.

Unfortunately I can't seem to get the Constraint.Implies() method working in my model.

To provide you with some context I have setup a simple demo: https://github.com/sandervanhooff1997/OptanoImpliesDemo. 

What I want to achieve in this demo is to build a conditional constraint with the Constraint.Implies() method:

- if a crop was planted on day 1

- no crops can be planted on day 2 + 3

- if a crop was planted on day 2

- no crops can be planted on day 3 + 4

- etc. etc.

Data:

- horizon of 9 days;

- 1 crop 'Crop A'.

Expected output:

day 1 Crop A

day 2 -

day 3 -

day 4 Crop A

day 5 -

day 6 -

day 7 Crop A

day 8 -

day 9 -

Actual output:

day 1 Crop A

day 2 Crop A

day 3 Crop A

day 4 Crop A

day 5 Crop A

day 6 Crop A

day 7 Crop A

day 8 Crop A

day 9 Crop A

Please look at the demo on Github to better understand the implementation in C#.

Kind regards,

Sander van Hooff

[OPTANO Team]

Well, I am not sure what's wrong with the code, example or glpk adapter.

(we are going to look into this).

You may use this patch to fix the implication on binaries:

---
 OptanoImplies/Program.cs | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/OptanoImplies/Program.cs b/OptanoImplies/Program.cs
index 8408d7a..50a2a44 100644
--- a/OptanoImplies/Program.cs
+++ b/OptanoImplies/Program.cs
@@ -47,20 +47,16 @@ namespace OptanoImplies
 
                         if (cropGrowing.Count() == 2)
                         {
-                            // crop assignment current crop on current day = 1
-                            var cropPlantedOnDayConstraint = new Constraint(CropAssignment[day, crop], "", 1, 1);
-
-                            // sum of crop assignment for all crops on next two days = 0
-                            var cropGrowingOnDaysConstraint = new Constraint(Expression.Sum(cropGrowing.SelectMany(d => crops.Select(c => CropAssignment[d, c]))), "", 0, 0);
-
-                            // if cropPlantedOnDayConstraint is fulfilled, cropGrowingOnDaysConstraint must also be fulfilled
-                            var impliesConstraint = cropPlantedOnDayConstraint.Implies(cropGrowingOnDaysConstraint);
-                            model.AddConstraint(impliesConstraint);
+                            // set otherDay to zero, if the crop is planted on day.
+                            foreach (var otherDay in cropGrowing)
+                            {
+                                model.AddConstraint(-CropAssignment[day, crop] + 1 >= CropAssignment[otherDay, crop]);
+                            }
                         }
                         else
                         {
                             // the crop can't finish before end of horizon
-                            var cropCantFinishGrowingConstraint = new Constraint(CropAssignment[day, crop], "", 0, 0);
+                            var cropCantFinishGrowingConstraint = CropAssignment[day, crop] == 0;
                             model.AddConstraint(cropCantFinishGrowingConstraint);
                         }
                     }
--
2.26.1.windows.1

Best,

jp

[s.vanho...@gmail.com]

Hi jp,

Thanks for your response.

For now I will implement your workaround and hope you succeed in providing a working solution using the implication.

I will check this post for updates from time to time.

[jannic...@optano.com]

Hi Sander,

we just released a new version of Optano Modeling, that should resolve this issue.

You can find it here: https://www.nuget.org/packages/OPTANO.Modeling/3.4.0.489

Best Regards,

Jannick