# Update initialization guesses on an existing problem without rebuilding?

**URL:** <https://discourse.julialang.org/t/update-initialization-guesses-on-an-existing-problem-without-rebuilding/137694>\
**Category:** Modelling & Simulations\
**Tags:** modelingtoolkit, mtk\
**Created:** [June 19, 2026, 11:06am UTC](https://discourse.julialang.org/t/update-initialization-guesses-on-an-existing-problem-without-rebuilding/137694 "2026-06-19T11:06:55Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Bart\_van\_de\_Lint](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bart_van_de_lint/32/212161_2.png) [@Bart\_van\_de\_Lint](https://discourse.julialang.org/u/Bart_van_de_Lint)\
**Post date:** [June 19, 2026, 11:06am UTC](https://discourse.julialang.org/t/update-initialization-guesses-on-an-existing-problem-without-rebuilding/137694/1 "2026-06-19T11:06:55Z")

</div>

I have a DAE built with ModelingToolkit. Between solves I re-initialize from a new operating point. For variables that have an initial constraint\*I can update them in place via the `Initial` parameter:

```julia
prob.ps[Initial(x)] = 1.0 # or setp(prob, Initial(x))(prob, 1.0)

```

For the _algebraic_ unknowns I only provide `guesses` (they’re solved by the initialization, not constrained). I’d like to update those starting guesses between solves — but there doesn’t seem to be a settable equivalent to `Initial(x)` for guesses.

As far as I can tell I have to remake the entire problem, parameters used in guesses get pruned by mtkcompile and cannot be used.

Is there a lighter-weight, supported way to mutate the guess values on an existing problem (something like a `Guess(x)` parameter), or is remaking the problem the intended path?