Wrap matrix `copyto!` incorrect

[liamh]

When using copyto! with wrap_gsl_matrix, the result looks correct but it is not.

using GSL
mat = reshape([Float64(10*j+i) for i=1:2 for j=1:4],4,2)
matgsl = GSL.matrix_alloc(4,2)
copyto!(GSL.wrap_gsl_matrix(matgsl), CartesianIndices((4,2)), mat, CartesianIndices((4,2)))

Which gives the expected results for mat and GSL.wrap_gsl_matrix(matgsl)

4×2 Matrix{Float64}:
 11.0  12.0
 21.0  22.0
 31.0  32.0
 41.0  42.0

but e.g. the first column that's actually in the GSL matrix is not correct

[GSL.matrix_get(matgsl,i,0) for i=0:3]
4-element Vector{Float64}:
 11.0
 31.0
 12.0
 32.0

[liamh]

Actually, it doesn't have to do with copyto!; I got rid of that and still I must fix up the wrap_gsl_matrix() result. With solngsl being the GSL matrix pointer,

solnjl = GSL.wrap_gsl_matrix(solngsl)
soln = reshape(reshape(solnjl,size(solnjl,1)*size(solnjl,2)),size(solnjl,2),size(solnjl,1))'

[giordano]

Is that simply because GSL is row-major, while Julia is column-major? Having to transpose matrices when interacting with external libraries is pretty normal.

[liamh]

I believe it is. It would be nice if there were some kind of transpose-storage function, or at least a warning.