On Sun, May 31, 2009 at 9:08 PM, David Cournapeau < da...@ar.media.kyoto-u.ac.jp> wrote:
> Charles R Harris wrote: > > > > > > On Sun, May 31, 2009 at 7:18 PM, David Cournapeau > > <da...@ar.media.kyoto-u.ac.jp <mailto:da...@ar.media.kyoto-u.ac.jp>> > > wrote: > > > > Charles R Harris wrote: > > > > > > > > > On Sun, May 31, 2009 at 11:54 AM, rob steed <rjst...@talk21.com > > <mailto:rjst...@talk21.com> > > > <mailto:rjst...@talk21.com <mailto:rjst...@talk21.com>>> wrote: > > > > > > > > > Hi, > > > After my previous email, I have opened a ticket #1117 > (correlate > > > not order dependent) > > > > > > I have found that the correlate function is defined in > > > multiarraymodule.c and > > > that inputs are being swapped using the following code > > > > > > n1 = ap1->dimensions[0]; > > > n2 = ap2->dimensions[0]; > > > if (n1 < n2) { > > > ret = ap1; > > > ap1 = ap2; > > > ap2 = ret; > > > ret = NULL; > > > i = n1; > > > n1 = n2; > > > n2 = i; > > > } > > > > > > I do not know the code well enough to see whether this could > > just > > > be removed (I don't know c either). > > > Maybe the algorithmn requires the inputs to be length ordered? > I > > > will try to work it out. > > > > > > > > > If the correlation algorithm doesn't use an fft and is done > > > explicitly, then the maximum overlap for any shift is the length of > > > the shortest input. Swapping the arrays makes that logic easier to > > > implement, but it isn't necessary. > > > > But this logic is also wrong if the swapping is not taken into > > account - > > as the OP mentioned, correlate(a, b) is not equal to correlate(b, > > a) in > > the general case. The output is reversed in the second case > > compared to > > the first case. > > > > > > I didn't say it was *correctly* implemented ;) > > :) So I gave it a shot > > http://github.com/cournape/numpy/commits/fix_correlate > > (It took me a while to realize that PyArray_ISFLEXIBLE returns false for > array object. Is this expected ? The documentation concerning copyswap > says that it is necessary for flexible arrays, but I think it is > necessary for object arrays as well). > Don't know. PyArray_ISFLEXIBLE looks like a macro... #define PyArray_ISFLEXIBLE(obj) PyTypeNum_ISFLEXIBLE(PyArray_TYPE(obj)) #define PyTypeNum_ISFLEXIBLE(type) (((type) >=NPY_STRING) && \ ((type) <=NPY_VOID)) And the typecodes are '?bhilqpBHILQPfdgFDGSUVO'. So 'SUV' are flexible and O is not. I'm not clear on how correlate should apply to any of 'SUV' but it might be worth having it work for objects. > It still bothers me that correlate does not conjugate the second > argument for complex arrays... > It bothers me also... Chuck
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