equations in MIP model

Problems with modeling
Fady
User
User
Posts: 4
Joined: 2 weeks ago

equations in MIP model

Postby Fady » 1 week ago

Dear all,

I am trying a model using binary variables, the constraint equations contain a product of two variables as:
(1- x)*(1-y) =e= 0;
but i get error "Endogenous operands for * not allowed in linear models"
is there any way to solve this or another way rewrite the equation?
thanks

cladelpino
User
User
Posts: 40
Joined: 5 months ago

Re: equations in MIP model

Postby cladelpino » 1 week ago

Hi Fady,

If both x and y are binary variables, in practice what you are writing has the same feasible region (of course not the same relaxed feasible region) as an inclusive OR.

This is usually written:
x+y=g=1

Of course you have to think if there is a reason that constraint is written like that. It could be poor modeling practice or something else.

You CAN solve your original equation but you would need to use a MINLP solver. It's also common practice to reformulate products and it can be done in an exact way when one of the variable is continous and the other is discrete. Products of two discrete variables can usually be avoided by using constraints like the one I wrote above.

Hope to help!
Claudio

Fady
User
User
Posts: 4
Joined: 2 weeks ago

Re: equations in MIP model

Postby Fady » 1 week ago

Hi cladelpino,

using the MINLP solver solved the problem. Thanks a lot for your help.

Kind Regards,
Fady


Return to “Modeling”

Who is online

Users browsing this forum: No registered users and 1 guest