julia> using JuMP, Ipopt
julia> m=Model(solver=IpoptSolver())
Feasibility problem with:
* 0 linear constraints
* 0 variables
Solver is Ipopt
julia> @variable(m, 0 <= x <= π / 2)
x
julia> c = @constraint(m, x >= π / 3)
x >= 1.0471975511965976
julia> @NLobjective(m, Min, sin(x))
julia> solve(m)
This is Ipopt version 3.12.8, running with linear solver mumps.
... lines omitted ...
julia> getdual(c)
0.5000000071047659
julia> cos(π/3)
0.5000000000000001