## Nonlinear constraints in MINLP model

Problems with modeling
mbh
User Posts: 10
Joined: 1 year ago

### Nonlinear constraints in MINLP model

Hi all,
I have a mixed integer non linear model and now I am trying to reduce the number of nonlinear constraints because the model is very big and I keep getting infeasibilities or errors.

Two of the constraints that are non linear are as following:

const11(n).. p(n) =e= 1 - (1 + (d(n) / 229)) ** (-0.2);

const12(n).. il(n) =e= p(n) * y(n) ;

where d(n) and y(n) are choice variables.

I tried using grid point approximation but since the constranits are not seperable I had a hard time in grid point approximation.
Does anyone have any idea how to change these two nonlinear constraints into linear constraints?

Best,
Mary

bussieck
Moderator Posts: 349
Joined: 3 years ago

### Re: Nonlinear constraints in MINLP model

Without further knowledge about the type of variables, the size of n etc it's hard to recommend anything. The constraints are nonlinear and while there are ways to linearize something like this (e.g. piecewise linear approximation) it's hard to suggest something useful without more details.

-Michael

Monsef
User Posts: 3
Joined: 2 years ago

### Re: Nonlinear constraints in MINLP model

For linearizing the nonlinear equations, you can use piecewise modulation. Others, like you are getting an infeasible solution, try to check the boundaries of your variables. Your solution might be out of the feasible region.
Monsef Tahir