Re: [OctDev] Vectorizing code array modulo indexing

[Juan P. C. <car...@if...>]

On Wed, Oct 3, 2012 at 6:01 PM, Torbjörn Rathsman
<tor...@st...> wrote:
> Juan Pablo Carbajal skrev 2012-10-03 17:48:
>
>> On Wed, Oct 3, 2012 at 4:55 PM, Torbjörn Rathsman
>> <tor...@st...> wrote:
>>>
>>> Juan Pablo Carbajal skrev 2012-10-03 14:02:
>>>
>>>> On Wed, Oct 3, 2012 at 12:17 PM, Torbjörn Rathsman
>>>> <tor...@st...> wrote:
>>>>>
>>>>> 2012-10-02 22:12, Juan Pablo Carbajal skrev:
>>>>>>
>>>>>> On Tue, Oct 2, 2012 at 9:00 PM, Torbjörn Rathsman
>>>>>> <tor...@st...> wrote:
>>>>>>>
>>>>>>> Is this kind of thing possible to do without do it in a loop?
>>>>>>>
>>>>>>>       notes=[1 1 0 1 1 1 0 1 1 0 1 0]';
>>>>>>>       x=12.*log(f./440)./log(2);
>>>>>>>       spectrum=spectrum.*cos(pi.*x).^16.* notes( mod(round(x),12) + 1
>>>>>>> );
>>>>>>>
>>>>>>> f is a vector of 10^7 elements and I want to take each computed index
>>>>>>> and
>>>>>>> generate corresponding value from notes.
>>>>>>> _______________________________________________
>>>>>>> Help-octave mailing list
>>>>>>> Hel...@oc...
>>>>>>> https://mailman.cae.wisc.edu/listinfo/help-octave
>>>>>>
>>>>>> Can you give more details? I do not see a loop.
>>>>>> I see that you are multiplying spectrum by something and then saving
>>>>>> it back into spectrum. What is the initial value of spectrum.
>>>>>>
>>>>>> Sorry for not understanding.
>>>>>>
>>>>>>
>>>>> Implemented using a loop:
>>>>>
>>>>> notes=[1 1 0 1 1 1 0 1 1 0 1 0]';
>>>>>
>>>>> for k=1:N %N huge
>>>>>
>>>>> x=12.*log(f(k)./440)./log(2);
>>>>>       spectrum(k)=spectrum(k).*cos(pi.*x).^16.* notes( mod(round(x),12)
>>>>> +
>>>>> 1 );
>>>>>
>>>>> end
>>>>>
>>>>> I want to implement the same thing without a loop.
>>>>>
>>>> Hi,
>>>>
>>>> Always keep the mailing list in CC.
>>>>
>>>> Here is my attempt tp vectorize your code. I expanded it so that you
>>>> understand all the stages. You do not need to create all those
>>>> intermediate variables
>>>> http://agora.octave.org/snippet/hchr/
>>>>
>>>> Note that I am assuming that the variable spectrum exists, it is a
>>>> column and has length N.
>>>>
>>>> Hope this helps.
>>>>
>>>>
>>> It does not work. You forgot that f is a vector, so is x and x_mod. Now,
>>> trying to use x_mod as index, will not expand notes into a squarewavish
>>> function but just fail with
>>>
>>>   subscript indices must be either positive integers or logicals
>>
>> Hi,
>>
>> It works here. Can you please post your complete example in Agora
>> (agora.octave.org) so we can see where is the problem?
>>
>> Thanks
>>
>>
> It works, I think I accidently put -inf in x log(0) !

Solution working
http://agora.octave.org/snippet/hchr/

-- 
M. Sc. Juan Pablo Carbajal
-----
PhD Student
University of Zürich
http://ailab.ifi.uzh.ch/carbajal/