On Mon, Apr 2, 2012 at 10:57 PM, J Diviney <justd...@gmail.com> wrote:
> I have a series of arrays each with at least 1000 elements and each of which
> needs to be accessed by about 10 different functions for different purposes.
> I've declared them as global to make the code simpler and to avoid passing
> them as arguments when it's much simpler to pass indices.

> In any case, I've tried these things, ndarray declarations with buffer types
> just aren't working for me, regardless of where I make them.

> On 3 April 2012 06:53, Robert Bradshaw <rober...@gmail.com> wrote:

>> On Mon, Apr 2, 2012 at 10:38 PM, J Diviney <justd...@gmail.com> wrote:
>> > For this particular example, I don't need the variable as a global.
>> > However,
>> > it is needed for the project I'm doing.

>> If you really need this, you can assign to a local variable within
>> your function (and then re-assign on exiting if you didn't just change
>> it inplace).

>> > I realise that the ndarray declarations you've used are faster, but
>> > that's
>> > exactly my problem, they refuse to compile and I usually get a message
>> > saying:

>> > 'ndarray' is not a type identifier

>> Could you please send the smallest, complete example you can create
>> where you get this error?

>> > On 2 April 2012 16:32, Aronne Merrelli <aronne.merre...@gmail.com>
>> > wrote:

>> >> On Sun, Apr 1, 2012 at 3:49 PM, J Diviney <justd...@gmail.com> wrote:
>> >> > This is just a simple example of the imports I'm doing. Like I said
>> >> > the
>> >> > code
>> >> > is useless, I just wanted to show what I was having trouble with
>> >> > instead
>> >> > of
>> >> > uploading 500 lines of code and the files that go with it.
>> >> > That's odd, I just checked again, the importing of sqrt from the c
>> >> > library
>> >> > works fine for me. In any case, you can just replace that with:
>> >> > from math import sqrt.
>> >> > Once again, apologies if my description is lacking, haven't posted
>> >> > here
>> >> > before.

>> >> Correct - if you do:

>> >> from libc.math cimport sqrt

>> >> Then you are "done" - all later calls to sqrt(x) in your cdef function
>> >> will directly use the C function.

>> >> In your example code you - do you really need to pull in the variable
>> >> as a global? You are defining the variable outside of any cdef
>> >> function, which isn't really helpful IMO. I do not think you will be
>> >> able to access "start" from python, since python cannot directly
>> >> access cdef variables (only cdef functions). Plus, the first version
>> >> with the declared dimensions would be the fastest; you can do this
>> >> easily if you just cdef an additional input to the test function.
>> >> Specifically, replace this:

>> >> start=nu.zeros(10000,dtype=nu.float)
>> >> def run_test(int n_loops):
>> >>   global start
>> >>   ...

>> >> With the following:

>> >> def run_test2(int n_loops, nu.ndarray[nu.float_t, ndim=1] start):
>> >>   ...

>> >> If you also typedef the arr variable same way - specifically, replace:

>> >>    cdef nu.ndarray arr=nu.zeros(len(start),dtype=nu.float)

>> >> With this (I like to make this 2 steps, it is clearer to me):

>> >>    cdef nu.ndarray[nu.float_t, ndim=1] arr
>> >>    arr=nu.zeros(len(start),dtype=nu.float)

>> >> The cython version is then substantially faster - here is a timing
>> >> result on my machine (I put those functions into dummy.pyx):

>> >> In [14]: %timeit dummy.run_test(10)
>> >> 10 loops, best of 3: 193 ms per loop

>> >> In [15]: %timeit dummy.run_test2(10,np.zeros(10000))
>> >> 1000 loops, best of 3: 996 us per loop

>> >> Hope that helps,
>> >> Aronne