[Numpy-discussion] Array views

srean srean.list@gmail....
Sat Mar 26 15:16:13 CDT 2011


Ah! very nice. I did not know that numpy-1.6.1 supports in place 'dot', and
neither the fact that you could access the underlying BLAS functions like
so. This is pretty neat. Thanks. Now I at least have an idea how the sparse
version might work.

If I get time I will probably give numpy-1.6.1 a shot. I already have the
MKL libraries thanks to free version of epd for students.


On Sat, Mar 26, 2011 at 2:34 PM, Pauli Virtanen <pav@iki.fi> wrote:

>
> Like so:
>
>    # Fortran-order for efficient DGEMM -- each column must be contiguous
>    A = np.random.randn(4,4).copy('F')
>    b = np.random.randn(4,10).copy('F')
>
>    def updater(b, col_idx):
>         # This will work in Numpy 1.6.1
>        dot(A, b[:,col_idx].copy(), out=b[:,col_idx])
>
> In the meantime you can do
>
>    A = np.random.randn(4,4).copy('F')
>    b = np.random.randn(4,10).copy('F')
>
>    from scipy.lib.blas import get_blas_funcs
>    gemm, = get_blas_funcs(['gemm'], [A, b]) # get correct type func
>
>    def updater(b, col_idx):
>         bcol = b[:,col_idx]
>        c = gemm(1.0, A, bcol.copy(), 0.0, bcol, overwrite_c=True)
>        assert c is bcol # check that it didn't make copies!
>
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