Re: Problems with FFT and IFFT

[Joe Koski]

on 2/28/06 1:24 PM, Quentin Spencer at address@hidden wrote:

> Joe Koski wrote:
> 
>> on 2/28/06 12:27 PM, John W. Eaton at address@hidden wrote:
>> 
>>  
>> 
>>> On 28-Feb-2006, Sascha Berkenkamp wrote:
>>> 
>>> | Must I set all values smaller than eps to zeros?
>>> 
>>> You can do that if you think it is appropriate for your application.
>>> I see no way that Octave can determine whether it is reasonable to do
>>> that for you.
>>> 
>>> jwe
>>> 
>>>    
>>> 
>> 
>> A related question:
>> 
>> Code efficiency-wise, would it be quicker to just x2=abs(x2), rather than
>> searching through eps values? The error introduced would probably be small.
>> Is there a quick vector way of setting all values less than eps to zero,
>> rather than searching the vector with a for loop?
>>  
>> 
> 
> Something like this:
> 
> octave:1> a=1:4;
> octave:2> a(a<=2)=0;
> octave:3> a
> a =
> 
>   0  0  3  4
> 
> 
> -Quentin
> 

Quentin, et al,

That's exactly the type of behavior I was looking for, e.g.

octave:4> a_true_mean = mean(a)
a_true_mean = 0.41590
octave:5> a_mean = mean(a(a <= 0.5))
a_mean = 0.14019
octave:6> ab_mean = mean(a(b<=0.5))
ab_mean = 0.30645

etc.

I had seen this used, so I knew it was in there somewhere. It is powerful,
and just what I need for a particular application. Where in the Octave
Manual or elsewhere is this construct documented? I looked but couldn't find
it. If they're not there already, I think some examples of this usage
somewhere would be useful.

Joe
 




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