# How to improve performance in a function that repeatedly defines and multiplies matrices

**URL:** <https://discourse.julialang.org/t/how-to-improve-performance-in-a-function-that-repeatedly-defines-and-multiplies-matrices/108153>\
**Category:** Julia at Scale\
**Tags:** performance, parallel, linearalgebra, complex-numbers, matrix\
**Created:** [December 29, 2023, 9:47am UTC](https://discourse.julialang.org/t/how-to-improve-performance-in-a-function-that-repeatedly-defines-and-multiplies-matrices/108153 "2023-12-29T09:47:43Z")\
**Posts on this page:** 1\
**Showing post:** 30

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**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [January 4, 2024, 7:51am UTC](https://discourse.julialang.org/t/how-to-improve-performance-in-a-function-that-repeatedly-defines-and-multiplies-matrices/108153/30 "2024-01-04T07:51:09Z")

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> [@Uranium238](#):
>
> Then why would someone ever use the `inv()` call?

Indeed, in most cases you don’t want to use `inv`, but there are cases where you do. For example, if you plan to re-use the same `inv(A)` over and over many times, then the one-time cost of inversion may be worth it (though, then you may still be better off using some matrix factorization). Or perhaps the inverse is of interest in its own right, not just as an intermediate step while solving equations.

> [@Uranium238](#):
>
> Why would anyone ever use the default library ?

It’s related to software licenses, MKL’s license is not fully compatible with the MIT license favored in the Julia community. You are free to use it, though.

> [@MKL: what are the issues these days?](https://discourse.julialang.org/t/mkl-what-are-the-issues-these-days/18191):
>
> I understand the JuliaPro does not ship MKL version anymore. There is an explanation of the situation in 2016 by @StefanKarpinski : This is not a technical issue primarily, it’s a legal one. You can easily build Julia with MKL, but as long as Julia ships with GPL libraries like FFTW and SuiteSparse, shipping Julia with MKL is illegal. Non-GPL licenses for both FFTW and SuiteSparse can be purchased, but obviously that’s not a viable open source default. If you’re willing to pay for a commerciall…

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