[Numpy-discussion] speed up np.diag

Citi, Luca lciti@essex.ac...
Fri Jul 10 10:16:14 CDT 2009


>>         if v.flags.f_contiguous:
>>             v, k, s = v.T, -k, s[::-1]

>Is this correct? The .flat iterator always traverses the array in virtual 
>C-order, not in the order it's laid out in memory.

The code could work (and gives the same results) even
without the two lines above which in theory do nothing:
taking the k-th diagonal of an array or the (-k)-th of
its transpose should be the same.
But in this case ndarray.flat works faster if the
array is C-contiguous.

Best,
Luca


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