# Physical units in Julia

**URL:** <https://discourse.julialang.org/t/physical-units-in-julia/76825>\
**Category:** General Usage\
**Tags:** unitful\
**Created:** [February 20, 2022, 11:18pm UTC](https://discourse.julialang.org/t/physical-units-in-julia/76825 "2022-02-20T23:18:16Z")\
**Posts on this page:** 1\
**Showing post:** 15

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**Author:** ![tim.holy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tim.holy/32/52_2.png) [@tim.holy](https://discourse.julialang.org/u/tim.holy)\
**Post date:** [February 21, 2022, 10:14am UTC](https://discourse.julialang.org/t/physical-units-in-julia/76825/15 "2022-02-21T10:14:21Z")

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Specifically on the topic of arrays with unitful entries: I do think we need a special array package for that. The point is that, e.g., linear algebra only makes sense for certain arrays, where the units are a cartesian product of unitful vectors for each axis. You can see that quite easily: with

\sum\_j A\_{ij} x\_j

you can only add the terms together if A\_{ij} x\_j all have the same units for each j. Consequently, the units of A\_{ij} must be given by u\_i v\_j where {\bf u} and {\bf v} are unitful-vectors (and where v\_j x\_j has units that are independent of j).

So really unitful arrays should be handled as dimensionless arrays with axis-vectors of units.

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