
Linear Regression 3 Ways in Julia - luu
http://boss-level.com/?p=247
======
therobot24
every time i see a Julia post i want to convert my Matlab code and start anew
- then i remember seeing a blog some time ago where the vectorizations i
performed to speed up my Matlab code would be faster as for-loops in Julia. Is
this still the case? If not, i'll probably consider the task much more
seriously

~~~
asg
That is still the case.

The following blog post goes into the reasons, and the remedies. In
particular, there are ways to automatically devectorise your code.

[http://julialang.org/blog/2013/09/fast-
numeric/](http://julialang.org/blog/2013/09/fast-numeric/)

~~~
blt
devectorizing is a terrible step back in expressiveness. It shouldn't be hard
to make a compiler that can compute the example without a bunch of temporary
arrays. I would be shocked if heavy duty packages like Matlab make all those
temporary arrays.

On the other hand, I've seen (and written) plenty of code that went through
contortions to use vector operations in IDL
([http://en.wikipedia.org/wiki/IDL_(programming_language)](http://en.wikipedia.org/wiki/IDL_\(programming_language\))).
It would be great to have a language where for loops _and_ vector expressions
are fast.

~~~
StefanKarpinski
Matlab does in fact make all those temporary arrays. So does R. See my comment
above [1] – the idea is not that you _should_ devectorize everything, but that
you can if you need to. Automatic devectorization of general purpose code is
not something anyone knows how to do – even in Haskell, which is the best
candidate language for such things – see moomin's comment below [2].

[1]
[https://news.ycombinator.com/item?id=6341406](https://news.ycombinator.com/item?id=6341406)

[2]
[https://news.ycombinator.com/item?id=6341187](https://news.ycombinator.com/item?id=6341187)

------
StefanKarpinski
The julia-users mailing list discussion of this blog post:

[https://groups.google.com/forum/#!topic/julia-
users/T5YYKQzl...](https://groups.google.com/forum/#!topic/julia-
users/T5YYKQzl-Cc)

------
tomrod
I'm impressed that these characters can be used in code:

Σ₁,Σ₀, σ²

~~~
Derbasti
Many moder programming languages allow arbitrary unicode symbols as variable
names. I am now thinking about doing this in Python.

~~~
tomrod
Fair enough. I use Sublime and write in python on Ubuntu. How might I go about
incorporating Unicode?

~~~
Derbasti
Hmm, here's a thought: Instead of naming a function "sum", call it Σ, and
similarly use √ instead of "sqrt". This would enable you to write things like

rms = √(1/len(x)*Σ(x))

Which is really quite cool from a mathematical view point.

