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How to limit the range of an index properly

  • 28 November 2020
  • 6 replies
  • 106 views
J

Dear All,

I have a question on how to limit the range of an index and since I’m new to Aimms I can’t find a proper solution. I just want to limit certain indices to a certain range for a specific constraint.

First example (Constraint):

Index Domain:t

Definition: e(t) <= e(t-1) |t<Tmax |t>Tmin

Error Message:

In an inclusion only the middle term is allowed to contain variables, however in the inclusion e(t) <= e(t-1) $ t < Tmax $ t the left term contains variables.

 

Second Example (Constraint):

Index Domain: (i,j,k,t)

Definition: r(i,j,k,t) <= o(i,k-1,t-1)*RM(i,j) |k>1|t>1

Error Message: The operators <= and > should to be the same for numerical inclusion (or use parenthesis).

 

As I’m new to aimms I dont seem to understand the principles properly. May someone point me to the right way to do this?

Thank you very much in advance!

Best Regards

Jonas

 

 

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Best answer by Gertjan 29 November 2020, 11:45

You should specify the conditions in the index domain. For example, for the first:

 

    Index Domain: t | (Tmin < t < Tmax)

    Definition: e(t) <= e(t-1)

 

The condition depends a little on how you specified the time set with index t. If they are a set of integer values this works; if they are more something like tp-001… tp-100 or some other named period, you would need to use the ord(t) function to count the element number. Eg 

 

    Index Domain: t | (Tmin < ord(t) < Tmax)

    Definition: e(t) <= e(t-1)
 

in above cases the constraint generation will only by for those t that fall within the condition specified.

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6 replies

Gertjan
Rank
Userlevel 6

You should specify the conditions in the index domain. For example, for the first:

 

    Index Domain: t | (Tmin < t < Tmax)

    Definition: e(t) <= e(t-1)

 

The condition depends a little on how you specified the time set with index t. If they are a set of integer values this works; if they are more something like tp-001… tp-100 or some other named period, you would need to use the ord(t) function to count the element number. Eg 

 

    Index Domain: t | (Tmin < ord(t) < Tmax)

    Definition: e(t) <= e(t-1)
 

in above cases the constraint generation will only by for those t that fall within the condition specified.

Gertjan, Product Owner AIMMS
Andrew
Rank

@jounas 

Were you able to figure out the solution to your question based on Gertjan’s response?

 

Andrew | User Support Engineer
J

Thank you for your answers! I was able to solve the problem!

J

I have one follow up question:

I have a set (index i,j) with four elements: A,B,C,D

I want two access A,B and C,D separatly in a constraint.

First I tried to limit the index domain of the constraint like this:

(i) | (3> ord(i)) so that i just uses A and B

Definition: o(i)=EF(i)-sum(j|(2 > ord(j)),r(i,j)) so that j uses C and D

 

Secondly I tried to use subsets:

Subset 1 Elements: A and B and index i

Subset 2 Elements: C and D and index j

Constraint:

Index Domain: (i,j)

Definition: o(i)=EF(i)-sum(j,r(i,j))

 

There was no error occuring but it seems like the program isn’t working as expected.

Therefore I would like to inquire on how to do this correctly.

 

Thank you again for your answers!

Best regards,

Jonas

 

J

Or to specify my question further:

How can I use the the index of a base set and limit it to the scope of a subset?

And how do I use default binding in this context?

Gertjan
Rank
Userlevel 6

Hi @jounas ,

You are not adding full context, so not sure if answer below is sufficient. Anyhow, your ideas posted about sound perfectly fine; guess it’s about fixing some details. Here some more info for you that I think will help:

  1. Limiting scope of constraint index could be done using index ( i | ord(i) <= 2 ) to get A and B. You could also (if elements are fixed) just use actual values ( i | i = ‘A’ or i = ‘B’)
  2. You could index also use subsets. Just make sure these subsets have their own index; so e.g subset1AB with index i_1, j_1 and subset2CD with index i_2,j_2. Now you can use those subset indices to specify the range of a constraint (over i_1) or the limited sum-calculation (over i_2)

Please notice that now the master set {A,B,C, D} has indices i, j while subsets have and underscore with respectively _1 (subset {A,B}) and _2 (subset {C,D}). No need to have a constraint over both indices; just i (or if over subset i_1 or i _2) is sufficient. You can use the j for the summations.

 

Hope it does help.

 

PS: Best to start a new thread for a new question to assure the community sees it and can reply (instead to adding it below this ‘solved’ question).

 

 

 

 

 

 

Gertjan, Product Owner AIMMS

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