[Haskell-cafe] Re: Patrick Perry's BLAS package

[Xiao-Yong Jin]

(Sorry, Patrick.  I forgot to CC haskell-cafe.)

Salute!  Excellent!

Patrick Perry <patperry at stanford.edu> writes:

> Wow, thanks for noticing, Alberto!  For anyone interested, I put up a
> formal announcement describing the bindings a little bit here:
>
> http://quantile95.com/
>
> I just registered the domain yesterday, so it may take a few days to
> resolve the DNS magic.  Here's the text of the announcement:
>

The magic is working, now.

>
> I’m really happy that people seem to be interested in the
> library. Alberto, in particular, is the primary author of hmatrix,
> another  haskell linear algebra library (which I stole a few ideas
> from), so if  he endorses it, that means a lot to me.
>
> So, Yet Another Linear Algebra Library? I’ve already mentioned
> hmatrix. There’s also another one called HBlas. Why would anyone want
> a third? Here are my reasons:
>
> 	* Support for both immutable and mutable types. Haskell tries
> to make you use immutable types as much as possible, and indeed there
> is a  very good reason for this, but sometimes you have a 100MB
> matrix, and  it just isn’t very practical to make a copy of it every
> time you  modify it. hmatrix only supports immutable types, and HBlas
> only  supports mutable ones. I wanted both.

I didn't use hmatrix a lot, because I wrote some STUArray
things and I wasn't sure what to do with that.  However, I
just noticed that there is a bunch of ST growing under
Data.Packed in hmatrix.  Guess things is going to change,
soon.  And perhaps with your work, Alberto doesn't need to
reinvent the wheel anymore.

> 
> 	* Access control via phantom types. When you have
> immutable and mutable types, it’s very annoying to have
> separate functions for each type. Do I want to have to
> call “numCols” for immutable matrices and “getNumCols” for
> mutable ones, even though both functions are pure, and
> both do exactly the same thing? No. If I want to add an
> immutable matrix to a mutable one, to I want to first call
> “unsafeThaw” on the immutable one to cast it to be
> mutable? No. With the phantom type trick, you can get
> around this insanity. Jane Street Capital has a very good
> description of how this works.  

Lovely!

> * Phantom types for matrix and vector shapes. This is a
> trick I learned from darcs. It means that the compiler can
> catch many dimension-mismatch mistakes. So, for instance,
> a function like foo :: (BLAS1 e) => Matrix (m,n) e ->
> Matrix (n,k) e -> Int -> Vector m e foo a b i = let x =
> row b i in a <*> x will not type-check. (”<*>” is the
> function to multiply a matrix by a vector. Everything is
> ok if you replace “row” by “col”.) This feature has caught
> a few bugs in my code.

If I understand this correctly, the compiler can catch
dimension mismatches so that using `col' will result in a
compilation error when m and k are different, is it so?

>
> LAPACK support is on the horizon, but that may take awhile. Also, I
> probably won’t do more than SVD, QR, and Cholesky, since those are all
> I need. Expect a preliminary announcement by the end of the summer.
>
> This work would not have been possible without looking at the other
> excellent linear algebra libraries out there. In particular the GNU
> Scientific Library was the basis for much of the design. I also drew
> inspiration from hmatrix and the haskell array libraries.
>
> Please let me know if you have any success in using the library, and
> if you have any suggestions for how to make it better.

I haven't look through the code, yet.  But it looks like
there are certain levels of similarities between blas and
hmatrix.  Is it possible for these two libraries to
cooperate well with each other?  (I didn't look at HBlas, so
can't say much about that.)

Apart from some warnings, the library compiles fine in my
system.  But there is a minor issue about the library it
links against when `./Setup test'.  I need to use `-lcblas'
instead of `-lblas' to get it to link to correct libraries.
I don't know other people's system.  But in my system,
Gentoo Linux, I use blas library provided by atlas, and
libblas.so is a fortran library and libcblas.so is for C.

All in all, good job.  Thanks.

Xiao-Yong
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