# JuMP.NLPEvaluator output format
**URL:** https://discourse.julialang.org/t/jump-nlpevaluator-output-format/16280
**Category:** Optimization (Mathematical)
**Tags:** documentation, jump
**Created:** [October 13, 2018, 4:47pm UTC](https://discourse.julialang.org/t/jump-nlpevaluator-output-format/16280 "2018-10-13T16:47:07Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@astor87](https://discourse.julialang.org/u/astor87)
#### Post date: [October 13, 2018, 4:47pm UTC](https://discourse.julialang.org/t/jump-nlpevaluator-output-format/16280/1 "2018-10-13T16:47:07Z")
I am trying to evaluate my constraints from my nonlinear program using IPOPT. From this discussion ([https://groups.google.com/forum/#!searchin/julia-opt/evaluating$20constraints%7Csort:date/julia-opt/m1ObRwgrvGE/Mo8bjsZ1AwAJ](https://groups.google.com/forum/#!searchin/julia-opt/evaluating%2420constraints%7Csort:date/julia-opt/m1ObRwgrvGE/Mo8bjsZ1AwAJ)), I am trying to use MathProgBase.eval\_g. The first line in calling this is
```julia
d = JuMP.NLPEvaluator(m)
```
I cannot find resources that describe how to interpret the output of this function call. First it lists the number of constraints and variables. After that, it shows a lot of numbers, #undef, and true/false statements–this is the part I am confused about. Is there a detailed description or examples somewhere of interpreting this?
The versions I am using are: Julia v0.6.4 and JuMP v0.18.2.
---
### Author:  [@miles.lubin](https://discourse.julialang.org/u/miles.lubin)
#### Post date: [October 14, 2018, 4:48am UTC](https://discourse.julialang.org/t/jump-nlpevaluator-output-format/16280/2 "2018-10-14T04:48:23Z")
Please see [Nonlinear Modeling — JuMP -- Julia for Mathematical Optimization 0.18 documentation](http://www.juliaopt.org/JuMP.jl/0.18/nlp.html#querying-derivatives-from-a-jump-model). `JuMP.NLPEvaluator()` returns an _opaque_ object that implements an interface (described in the JuMP and MathProgBase docs). There’s not much to be gained by trying to look inside the object.