# Understanding NLSolvers Package through the Given Documentation

**URL:** <https://discourse.julialang.org/t/understanding-nlsolvers-package-through-the-given-documentation/82512>\
**Category:** General Usage\
**Tags:** question, package, nlsolve\
**Created:** [June 9, 2022, 4:22pm UTC](https://discourse.julialang.org/t/understanding-nlsolvers-package-through-the-given-documentation/82512 "2022-06-09T16:22:07Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![MJF](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@MJF](https://discourse.julialang.org/u/MJF)\
**Post date:** [June 9, 2022, 4:22pm UTC](https://discourse.julialang.org/t/understanding-nlsolvers-package-through-the-given-documentation/82512/1 "2022-06-09T16:22:07Z")

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I am quite new to Julia and trying to figure out how to use the NLSolvers package as given in the following link: [NLSolvers](https://github.com/JuliaNLSolvers/NLSolvers.jl/blob/master/README.md)

In the README file, they provide an example for a nonlinear system of equations for the Rosenbrock model problem. I understand what the first two functions are doing – providing the equations and then the Jacobian of the system.

My confusion is about the last function: Jvop\_rosenbrock!. I cannot figure out what this is and how they determined what Fv should be.

I want to take this example and apply it to a nonlinear system of 6 equations. Any ideas on what this function is doing and how it relates to the Rosenbrock problem. Thanks!