I am playing with Couenne for NLP optimization problems with JuMP and AmplNLWriter. After setting up these packages, I tried the toy example in Couenne’s documentation (section 5). For convenience, the problem is posted here.

My Julia code is shown below.

```
using JuMP, AmplNLWriter
model = Model(with_optimizer(AmplNLWriter.Optimizer, raw"C:\Users\Gao Shuhua\Downloads\couenne-win64/couenne.exe"))
@variable(model, 0<=x0<=10)
@variable(model, 0<=x1<=10)
@variable(model, y2, Bin)
@variable(model, y3, Bin)
@variable(model, y4, Bin)
@constraints(model, begin
y2 + x0 <= 1.6
y3 + 1.333*x1 <= 3
y4 - y3 - y2 <= 0
end)
@NLconstraint(model, x0^2 + y2 == 1.25)
@NLconstraint(model, x1^1.5 + 1.5*y3 == 3)
@objective(model, Min, 2*x0 + 3*x1 + 1.5*y2 + 2*y3 - 0.5*y4)
optimize!(model)
```

The last line `optimize!(model)`

displays the following information:

```
Couenne 0.5.7 -- an Open-Source solver for Mixed Integer Nonlinear Optimization
Mailing list: couenne@list.coin-or.org
Instructions: http://www.coin-or.org/Couenne
couenne:
ANALYSIS TEST: Error evaluating constraint 2: can't evaluate pow"(0,1.5).
```

and then terminated. The termination status is

```
termination_status(model) = MathOptInterface.OTHER_ERROR
objective_value(model) = NaN
```

In contrast, the problem has been solved successfully in the documentation. Is there anything wrong in my code, or did I missing anything? Thank you.