# Independent variable t - @parameter or @variable?

**URL:** <https://discourse.julialang.org/t/independent-variable-t-parameter-or-variable/69619>\
**Category:** Modelling & Simulations\
**Tags:** modelingtoolkit\
**Created:** [October 12, 2021, 12:59pm UTC](https://discourse.julialang.org/t/independent-variable-t-parameter-or-variable/69619 "2021-10-12T12:59:16Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![SCher](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/scher/32/20477_2.png) [@SCher](https://discourse.julialang.org/u/SCher)\
**Post date:** [October 12, 2021, 12:59pm UTC](https://discourse.julialang.org/t/independent-variable-t-parameter-or-variable/69619/1 "2021-10-12T12:59:16Z")

</div>

While creating models in MTK for a system of ODEs, should time t be specified as a @parameter or @variable? I have seen different examples use both ways, and both seem to work. Which is recommended? Any particular reasons?  
Thanks.

---

<div class="post-metadata">

**Author:** ![PikaPei](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pikapei/32/16872_2.png) [@PikaPei](https://discourse.julialang.org/u/PikaPei)\
**Post date:** [October 15, 2021, 2:37pm UTC](https://discourse.julialang.org/t/independent-variable-t-parameter-or-variable/69619/2 "2021-10-15T14:37:29Z")

</div>

There’s a related topic.  
[https://github.com/SciML/ModelingToolkit.jl/issues/183](https://github.com/SciML/ModelingToolkit.jl/issues/183)