[Numpy-discussion] avoiding the matrix copy performance hit

Tim Hochberg tim.hochberg at cox.net
Wed Feb 15 09:15:02 CST 2006


Ed Schofield wrote:

>Travis Oliphant wrote:
>
>  
>
>>I think I originally tried to make mat *not* return a copy, but this
>>actually broke code in SciPy.  So, I left the default as it was as a
>>copy on input.  There is an *asmatrix* command that does not return a
>>copy...
>>    
>>
>
>All SciPy's unit tests actually pass with a default of copy=False in the
>matrix constructor.  So SciPy needn't be the blocker here.  I'd like to
>cast a vote for not copying by default, in the interests of efficiency
>and, as Bill Baxter argued, usefulness.
>  
>
I would like to cast a vote for keeping the behaviour the same. Note that:

mat([[1,2,3], [3,4,5]])

will always create a copy of its data by necesesity. Which means that 
changing the default copy=False means that some data will be copied, 
while others will not be, potentially leading to subtle bugs. I strongly 
disaprove of this sort of inconstent behaviour (don't get me started on 
reshape!).

In this situation, people should just use asmatrix.

-tim


>-- Ed
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