# Use of save\_idxs solver option with MethodOfLines/ModelingToolkit

**URL:** <https://discourse.julialang.org/t/use-of-save-idxs-solver-option-with-methodoflines-modelingtoolkit/92023>\
**Category:** Modelling & Simulations\
**Created:** [December 22, 2022, 9:35pm UTC](https://discourse.julialang.org/t/use-of-save-idxs-solver-option-with-methodoflines-modelingtoolkit/92023 "2022-12-22T21:35:25Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![johnb](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/johnb/32/44115_2.png) [@johnb](https://discourse.julialang.org/u/johnb)\
**Post date:** [December 22, 2022, 9:35pm UTC](https://discourse.julialang.org/t/use-of-save-idxs-solver-option-with-methodoflines-modelingtoolkit/92023/1 "2022-12-22T21:35:25Z")

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I’m trying to use save\_idxs to facilitate parameter fitting and while I’ve figured out that my solution needs to be accessed after solving as:

```julia
sol.u[var1(x,t)][idx1,idx2]

```

I’m having trouble figuring out how to use the save\_idxs=[idx\_to\_be\_saved] solver option.

Is there new syntax for this?

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**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [December 22, 2022, 10:48pm UTC](https://discourse.julialang.org/t/use-of-save-idxs-solver-option-with-methodoflines-modelingtoolkit/92023/2 "2022-12-22T22:48:40Z")

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Open an issue. I don’t think that works with the PDE indexing right now.

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<div class="post-metadata">

**Author:** ![johnb](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/johnb/32/44115_2.png) [@johnb](https://discourse.julialang.org/u/johnb)\
**Post date:** [December 22, 2022, 10:54pm UTC](https://discourse.julialang.org/t/use-of-save-idxs-solver-option-with-methodoflines-modelingtoolkit/92023/3 "2022-12-22T22:54:08Z")

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Okay, will do. Since save\_idxs is from the DifferentialEquations.jl package, I will open it there.

Thanks!