How to use a decision variable from optimization problem into an if else statement?

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Paramvir Singh 2018-4-29

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评论： Amir Hossein Nazeri 2022-4-5

Here Tins is a decision variable of size=(24,1) in my optimization problem. The value of Tins(min_des) =20 while value of Tins(max_des) = 23. When I input the if else statement using Tins variable for value comparison, then the following error is shown by matlab:-

Please suggest the corrective measure. Thanks in advance

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Paramvir Singh 2018-5-1

Is the information provided regarding the problem not sufficient?

Matt J 2018-5-1

编辑：Matt J 2018-5-1

在 MATLAB Online 中打开

It's way too much. An optimization problem has the following form

min f(x)
subject to g(x)<=0, h(x)=0

I'm looking for you to tell me, in your case, what x,f,g,and h are.

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采纳的回答

Mary Fenelon 2018-5-2

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The if-constraints (logical constraints, implication constraints) can be modeled with linear constraints and binary variables.

To see how to do this, suppose you have a binary variable y that should be 1 when x > 0. The constraint x - M*y <= 0, where M is an upper bound on x, will enforce this. When x > 0, y must be 1; the only other possible value for y is 0 and if y were 0, the constraint reduces to x <= 0, a contradiction.

To formulate constraint (6), make two constraints

(Tmin - Tins) - M1*(1-BCac) <= 0 where M1 is an upper bound on (Tmin - Tins)
(Tins - Tmax) - M2*BCac <= 0 where M2 is an upper bound on (Tins - Tmax)

The resulting constraints are called big-M constraints or indicator constraints. The y variable is called an indicator variable.

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Paramvir Singh 2018-5-5

In the code for my constraint (6), I have another doubt if for a value of Tins=27, although second constraint is being satisfied, but for the first constraint, for Tins=27,

Both BCac=0 or 1 satisfy the constraint. I think due to this reason my intlinprog solver is not giving a feasible solution.

Any help in this regard would be appreciated.

Amir Hossein Nazeri 2022-4-5

@Paramvir Singh Hi Paramvir, Is your problem solved? Can you share your Matlab code with me if possible? Or if you have any Github or so...

Thanks!

Amir

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