**Edit1: Sorry i found lens next to avatar ^^**

Hello

Please can I ask newbie q, i need to make signum variable from another variable.

(tried things like type Int in variable type / sign function in constrains but get errors from solver/constrains)

But i am failing even with 2 state (0,1) variable:

```
using JuMP
using Ipopt
model = Model()
@variable(model, d)
@objective(model, Max, d )
@constraint(model, d^2 == d)
set_optimizer(model, Ipopt.Optimizer)
optimize!(model)
value(d)
```

EXIT: Optimal Solution Found.

d=0.0

But d can be 1 :-/

How is possible to do sign like behavior?

**Edit 2:**

tried

```
model = Model()
@variable(model, d)
@variable(model, x)
@objective(model, Max, d )
@constraint(model, (x) == 4.65)
#@constraint(model, abs(x) == d*x)
@constraint(model, d*x == abs(x))
```

ERROR: MethodError: no method matching abs(::VariableRef)

Thanks