slice of vector immutable/mutable?

[Daniel Korzekwa]

I just found a bug in my code, which was due to assuming that slice of vector in breeze is immutable (copy), but I just realized it's a view (read/write through).

- What is the reason behind this? Wouldn't it be better to create immutable slice by default? 

- In breeze doc (https://github.com/scalanlp/breeze/wiki/Linear-Algebra-Cheat-Sheet#indexing-and-slicing) it is stated that the corresponding matlab operation is a(2:5), lets point it out that in breeze it's just a view and not a copy. Oh, just found on the Quickstart breeze page this

'....The slice operator constructs a read-through and write-through view...'

[David Hall]

The reason is the usual: performance. It being immutable doesn't really solve the general problem, only being a copy does. But I'm not willing to sacrifice that performance.

I guess evidently it should be better documented.

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[Daniel Korzekwa]

yeah, I really meant a copy.

I actually like the performance wise approach, but still I would not be surprised others do similar mistake that me. I think that a good book on breeze would help. I made this mistake simply because of not understanding well how breeze works and how is it different from other linear algebra libraries. Any plans to write one?

[David Hall]

"Plans" is too strong a term. Aspirations is perhaps better. Maybe even "intentions." :-)

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