# Conditional constraint if else in JuMP

Hello,
How I can model the conditional constraint if else with JuMP in Julia ?

Thank you

You might be able to do that using Integer Programming techniques. Can you give an example of what you want to do?

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You might be interested in https://github.com/rdeits/ConditionalJuMP.jl.

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@tkoolen great work!. I was implementing indicator constraints myself which use native CPLEX and Gurobi functions. I just need to finish the @indicatorconstraint macro but everything else is done. Also check the Pyomo.gdp plugin which also implements some cool stuff like nested disjunctions and convex hull reformulations.

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Woah, that’s not my package; it’s all @rdeits’ work. But yeah, he’s doing great work!

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I also want to to the same something like this:

@NLconstraint(cgecam, eq[it in IT] , pm[it] == pwm[it]er(1 + tm[it]) if pwm[it]>=0.0 )

in otherwords I create a contraint only if pwm[it] is greater than zero. In GAMS it works well with \$ operator. For Julia/Jump I have failed to do this.

You can do this with complementarity constraints.
For instance, the following constrains `y = 1/2` if `x >= 0` but it also constrain `x` to be zero if `y` is not `1/2` which may or may not be what you want depending on your application.

``````@variable(model, x >= 0)
@constraint(model, 2y - 1 ⟂ x)
@constraint(model, 2y - 1 ⟂ x)
``````

Can you give a reference to the GAMS doc for this `\$` operator ?

Thanks for the quick response. Reference for the dollar operator is https://www.gams.com/latest/docs/UG_CondExpr.html. It is used a lot especially for computable general equilibrium models to ignore equations.

Now to put my question different–suppose x is not a variable in the model and its a parameter. How can I implement this
@constraint(model, eq[i in I], 2y[i] - 1, if x[i]>=0)

Am trying to figure out how to write this in short form because they are so many equations to use loops everywhere. The LDCO[j], KDCO[j]! are not variables but rather parameters computed from elsewhere.
for j in J
if LDCO[j]!=0 && KDCO[j]!=0
@NLconstraint(CGEModel,VA[j] == B_VA[j]*((beta_VA[j]*LDC[j]^(-rho_VA[j]))+((1-beta_VA[j])KDC[j]^(-rho_VA[j])))^(-1/rho_VA[j]))
elseif LDCO[j]!=0
@NLconstraint(CGEModel,VA[j] == B_VA[j]
(beta_VA[j]LDC[j]^(-rho_VA[j]))^(-1/rho_VA[j]))
elseif KDCO[j]!=0
@NLconstraint(CGEModel,VA[j] == B_VA[j]
((1-beta_VA[j])KDC[j]^(-rho_VA[j]))^(-1/rho_VA[j]))
end
end
If this was GAMS I would just write this using the dollar operators:
EQ3(j)… VA(j) =e= B_VA(j)
{
[beta_VA(j)*LDC(j)(-rho_VA(j))]\$LDCO(j)
+[(1-beta_VA(j))*KDC(j)
(-rho_VA(j))]\$KDCO(j)
}**(-1/rho_VA(j));
How do i do something similar in Julia/JuMP.

It’s easier to help if you do the following:

• format your code using the triple backticks: `````
• provide a minimal working example of what you are trying to accomplish.
• Simplify it down to one constraint, and two or three variables. Remove any redundant information.
• It may help to provide the math formulation of your simple problem as well.
• What solver are you using? If you are trying to solve MPEC-type models, JuMP is a little behind compared to GAMS. You either have to do the reformulations manually, or using a solver like KNITRO.jl.
• You could also use a mixed-integer reformulation.

The simpler version of my problem is as follows.
@NLconstraint(model, eq[i in I], 2y[i]^3 - 1, if x0[i]>=0
where x0 is a parameter. In otherwords how does NLconstraint accomodate if statements

This is not a constraint. Do you mean

``````@NLconstraint(model, eq[i in I; x0[i] >= 0], 2y[i]^3 - 1 == x0[i])
``````

which is equivalent to

``````for i in I
if x0[i] >= 0
@NLconstraint(model, 2y[i]^3 - 1 == x0[i])
end
end
``````
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Perfect this is what I wanted. Thanks so much.

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