Re: Cython / c++ help

Hi Stéfan, Johannes, Thanks for having a read through this... I've tried to explain the reason why I shouldn't perform the prefix/cumulative sum on the CPU using numpy etc in this diagram... https://lh5.googleusercontent.com/-AhB5JfV8qQA/UaSk96a9jDI/AAAAAAAAAEY/MKD8i... In method 1 I have to ship the entire flag array, build the compacted array and ship it back. I've also tested cumsum with timeit and I'm certain the CPU prefix-sum algorithms are simply too slow..

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timeit.timeit('np.cumsum(x)', setup='import numpy as np; x = np.random.random_integers(0, 10, 1850)')

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8.654011964797974

Method 2 just requires that the length of the queue be shipped across to the CPU to know have many threads to execture the GPU method gpu_process_tiles() with. On Monday, May 27, 2013 11:54:50 PM UTC+2, Stefan van der Walt wrote:

On Mon, May 27, 2013 at 10:55 PM, Marc de Klerk javascript:

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wrote:

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This operation has to happen a lot… so I really need it to be fast. The problem I'm having is that the when I isolate and measure the execution time of the gpu code it's much faster than that of the c++ or Cython wrapper - which I cannot really do without.

Another option is also to call into the NumPy C API to evoke essentially the equivalent of

np.nonzero(np.diff(np.cumsum(x)))[0] + 1

Stéfan