# Simple symbolic equation manipulation with ModelingToolkit.jl

**URL:** <https://discourse.julialang.org/t/simple-symbolic-equation-manipulation-with-modelingtoolkit-jl/53130>\
**Category:** New to Julia\
**Tags:** symbolic, modelingtoolkit\
**Created:** [January 11, 2021, 12:57am UTC](https://discourse.julialang.org/t/simple-symbolic-equation-manipulation-with-modelingtoolkit-jl/53130 "2021-01-11T00:57:13Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Sciemon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sciemon/32/20897_2.png) [@Sciemon](https://discourse.julialang.org/u/Sciemon)\
**Post date:** [January 11, 2021, 12:57am UTC](https://discourse.julialang.org/t/simple-symbolic-equation-manipulation-with-modelingtoolkit-jl/53130/1 "2021-01-11T00:57:13Z")

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I simply would like to isloate a variable from an expression/equation, e.g.:

```julia
using ModelingToolkit
@variables a b c
eqs = 0 ~ a + b + c

```

I want to solve this for variable ‘a’ (isolate ‘a’ on the left hand side).  
As I understand, Modeling Toolkit is mainly intended for coupling of symbolic and numeric math and optimize the latter. However, I would like to use it for this kind of (or more complicated) equation solving instead of doing it by hand.  
Thanks!

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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:** [January 11, 2021, 1:49am UTC](https://discourse.julialang.org/t/simple-symbolic-equation-manipulation-with-modelingtoolkit-jl/53130/2 "2021-01-11T01:49:59Z")

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It’s not fully documented yet, but the alias elimination code is how we do it:

[https://github.com/SciML/ModelingToolkit.jl/blob/91043dc66f6e8fb8724060ef40ba8e4c0e04110e/src/systems/reduction.jl](https://github.com/SciML/ModelingToolkit.jl/blob/91043dc66f6e8fb8724060ef40ba8e4c0e04110e/src/systems/reduction.jl)

You might want to wait until it’s documented or use that to write the docs, taking into account any changes in [https://github.com/SciML/ModelingToolkit.jl/pull/720](https://github.com/SciML/ModelingToolkit.jl/pull/720)

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**Author:** ![Sciemon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sciemon/32/20897_2.png) [@Sciemon](https://discourse.julialang.org/u/Sciemon)\
**Post date:** [January 13, 2021, 11:57am UTC](https://discourse.julialang.org/t/simple-symbolic-equation-manipulation-with-modelingtoolkit-jl/53130/3 "2021-01-13T11:57:55Z")

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Thank you Chris! I am new to Julia and don’t understand what the function does exactly. So I’ll wait for the documenation.