Re: vectorization

[dbateman]

Ben Abbott wrote:
> 
> I took a look at this as well and would have responded earlier but my  
> internet went down during a thunderstorm :-(
> 
> David, of the three versions you posted only the third ran for me  
> without error. While the 3rd version does run, it does not give (what  
> I think) is the correct answer :-(
> 

Hey the third version worked!! None were tested which is why I had so much
trouble getting it right. However ...



> 
> octave:46> A = rand([1,9])
> A =
> 
>     0.90785   0.89152   0.74896   0.71078   0.21859   0.26943    
> 0.89706   0.63350   0.47987
> 
> octave:47> q = newfilter (A, 3)
> q =
> 
>     0.89152   0.89152   0.89152   0.26943   0.26943   0.26943    
> 0.63350   0.63350   0.63350
> 
> Unfortunately, a quick check of the first 3 elements gives a incorrect  
> result.
> 
> octave:48> mean (A(1:3))
> ans =  0.84944
> 
> The repmat approach had not occurred to me. The approach I took was  
> to ...
> 
>        a = mean (reshape(A, [npoints, numel(A)/npoints]));
>        q = reshape (ones (npoints, 1) * a, [1, numel(A)]);
> 
> Which (I believe) produces the desired result.
> 
> octave:49> q = newfilter (A, 3)
> q =
> 
>     0.84944   0.84944   0.84944   0.39960   0.39960   0.39960    
> 0.67014   0.67014   0.67014
> 

The original code indexes back to a copy of the original array elements and
not the mean, so I think my version is correct. Or rather it should have the
same behavior as the original function.

D.

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