[Ipopt] dual of a constraint

[Hossein Haghighat]

Hi all,
I use Ipopt to get the dual of a constraint in a NLP model in ampl. I have
also tried other solvers including Minos and Knitro to compare these value.
They give three different results.
can anybody tell me which value can be trusted? is there any method e.g.
problem reformulation or addition of extra terms to objective or
constraints, to get the same value from different solvers?
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