Handling transposed matrices in FFI calls

[acowley]

See the question and answer on SO.

[amcphail]

I'm referring this to the author of hmatrix

import Numeric.LinearAlgebra
import Numeric.GSL.Fitting.Linear

import Data.Packed.Development

test1 :: IO ()
test1 = do
  let y = fromList [1,2,3,4,5]
  let x = trans $ fromLists [[1,2,3,4,5], [1,1,1,1,1]]
  let x3 = fromLists [[1,1], [2,1], [3,1], [4,1], [5,1]]
  print $ x == x3
  print $ multifit x y
  print $ multifit x3 y

test2 :: IO ()
test2 = do
  let y = fromList [1,2,3,4,5]
  let x = cmat $ trans $ fromLists [[1,2,3,4,5], [1,1,1,1,1]]
  let x3 = fromLists [[1,1], [2,1], [3,1], [4,1], [5,1]]
  print $ x == x3
  print $ multifit x y
  print $ multifit x3 y

main :: IO ()
main = do
  test1
  putStrLn ""
  test2

[amcphail]

Comment from aruiz https://github.com/albertoruiz/hmatrix/issues/53

"trans" only flips the row major / column major order field, but it does not actually transpose the data:

https://github.com/albertoruiz/hmatrix/blob/master/lib/Data/Packed/Internal/Matrix.hs#L97

This is to avoid some unnecessary transpositions (e.g blas matrix multiply admits transposed arguments):

https://github.com/albertoruiz/hmatrix/blob/master/lib/Numeric/LinearAlgebra/LAPACK.hs#L61

But most wrappers need a fixed order, for instance:

https://github.com/albertoruiz/hmatrix/blob/master/lib/Numeric/LinearAlgebra/LAPACK.hs#L151

cmat and fmat are provided in Data.Packed.Development to force the required order in FFI calls. Here we have some examples:

https://github.com/albertoruiz/hmatrix/tree/master/examples/devel

[acowley]

Surely the requirement to put an argument in a fixed order should be the responsibility of the wrapper?

[amcphail]

Good point. Updated to hmatrix-gsl-stats 0.2