I’m a little sad, because it seems like we don’t have any packages for solving nonlinear equations (not odes, not pdes) on a domain range. An equivalent function in the MATLAB world is vpasolve() in which I can feed it a vector of functions, and I can specify the range in which the solution is. The …

[image] duncanam: As you can see, a+b needs to remain smaller than 10.95 per the formulation in Eq. 2 and Eq. 4. I know their values are between 1 and 5, so I need my solver to stay within these bounds. If you let c^2 = 5.475 - 0.5(a+b), couldn’t you change variables in your solver from (a,b) …

That is T? Do you have a minimal working example?

In principle this is possible using IntervalRootFinding.jl, but I guess only if hs is a Julia function. Please make a minimal example that we can run to define the functions.

Unfortunately, this package seems to not like my functions either when I set it up as you suggest: using NLPModels, NLPModelsIpopt function c(x) a = x[1] b = x[2] Tf = x[3] F = [kpc_lhs(Tf) - kpc_rhs(a,b); # Eq. 1 - Eq. 2 = 0 kph_lhs(Tf) - kph_rhs(a,b); # Eq. 3 - Eq. 4 = 0 …

This is an interesting approach, I’ll have to play around with it further. I should have known there was a better mathematical path. Thank you.

Is the issue that your x0, lcon and ucon are integer? Try making them float vectors.

Ah, that may have been it. It does run now, but oddly the solutions it is returning are outside the bounds given, so I will have to look at it further and see what the issue is. It also never converges, so that may be it (although I’m not surprised, everything is so nonlinear with each variable that…

Ipopt doesn’t guarantee that general constraints are satisfied at intermediate iterates. If that’s a requirement for you, you may want to try Knitro, which has a feasible mode. You can download an evaluation version and give it a go (see the link I posted above). Also, those solvers assume your prob…

Solve Constrained Nonlinear System (?)

General Usage

dpo May 7, 2020, 5:47am 5

See my answers to a very similar question here: Nonlinear System of Equations with Bounds/Constraints on Unknowns - #16 by dpo

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Solve Constrained Nonlinear System (?)

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