NonlinearSolve.jl: Possible to store solution in-place of initial guess?

Specific Domains Numerics
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The standard workfllow to access the solution of a nonlinear_eq = NonlinearProblem is something like

sol = SciMLBase.solve(nonlinear_eq, NewtonRaphson(autodiff = AutoFiniteDiff()));

Is it possible to suppress the build-up of the sol object and have the solution written directly to the initial guess which is supplied in construction of the NonlinearProblem?

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alias_u0 = true, though we’re rolling out a whole aliasing system to simplify this, so that will be deprecated very soon for just a more comprehensive verbose

CC @jClugstor

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Thanks!

I was also wondering if there is a way to pre-allocate the du for in-place functions f!(du, u, p)

I am calling the nonlinear solver from a hot loop, and would like to cut down allocations as far as possible.

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How big is your system? If it’s small, use static arrays and they all stack allocate with SimpleNonlinearSolve. If it’s big then these ones don’t matter: the Jacobian is O(n^2) vs these O(n). The general way to do the big ones would be to use the cache = init(prob) interface, though I’m cleaning that up a bit in order to get it documented so that might need to wait till over the weekend to have a fully non-allocating form.

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So eventually I would like to go to millions of unknowns, as I am trying to build a special IMEX-multirate integration scheme for Trixi.jl

Thanks, good to know! I was wondering how to go about this, since NonlinearProblem itself is immutable - which leads to me currently re-initializing it all the time despite only parameter and initial guess changes.

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I put a reminder to respnnd here next week, hopefully i get this done and will post

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