Re: [OctDev] Vectorizing code array modulo indexing

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

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.


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