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

Xiao-Yong Jin wrote:

Salute! Excellent!

Patrick Perry writes:

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* 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.

Sure, in the future the internal modules of hmatrix (if not all of them) can be replaced by Patrick's blas and the future lapack. And several alternative high level interfaces may coexist as thin layers on the underlying computational engine with different goals: from very simple interfaces for causal usage to advanced ones for more complex applications.

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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?

Yes, the compiler infers the type of expression to be

Matrix(m,n) e -> Matrix (l,m) e -> Int -> Vector n e

which is different from the declared type. The error will be something like "Expected type Vector m e, but got type Vector a1 e instead".

And if I understand it correctly, usage is also very practical. You can define something like listVector 3 [1,2,3::Double] and the dimension type is "free". But if you give a signature you get static dimension checking: listVector 3 [1,2,3] Vector TypeDim3 Double I like this approach very much. Which types do you recommend for the dimensions? User friendly static dimension checking must be available in any serious Haskell linear algebra library. Frederik Eaton also made very interesting work on this in his index aware library.

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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.)

This is more work than you might think. The data structures are different, many of the function names are different, and the module namespaces overlap. I wouldn't recommend any switch from hmatrix to blas right now unless you really need mutable types-- hmatrix has a lot more linear algebra functionality.

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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.

I don't know of a good way to get around this. It seems like every system has a different convention for the location and name of the cblas libraries. So, everyone has to edit the "extra-libraries" and the "extra-lib-dirs" field in the blas.cabal file. Does anyone know of a better way of doing this?

(sorry if you receive this again, a previous message seems to be lost) A possible solution is using flags in the cabal configuration file. For instance, I have this in hmatrix.cabal: if flag(mkl) if arch(x86_64) extra-libraries: gsl mkl_lapack mkl_intel_lp64 mkl_sequential mkl_core else extra-libraries: gsl mkl_lapack mkl_intel mkl_sequential mkl_core else extra-libraries: gsl blas lapack so if I want to link with Intel's MKL optimized blas/lapack instead of ATLAS I simply add the -fmkl flag: runhaskell Setup.lhs configure -fmkl etc. or even cabal install hmatrix -fmkl Other flags can be added to support different distributions. We could have something like cabal install package -ffedora or cabal install package -fcblas etc. Alberto