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Re: Approximate convolution - for loop problem [message #64415 is a reply to message #64414]

Sun, 21 December 2008 12:01

Sam
Messages: 4
Registered: March 1999

Junior Member

Hi David, unfortunately shift() does not do the business for me, as
these two examples below show. So I'm still a bit stumped here.

; Array operation I'm trying to execute.
a=[1.,2.,3.,4.]
for ii=1,3 do a[ii] += 0.5*a[ii-1]
print,a
1.00000 2.50000 4.25000 6.12500

; Attempt to perform this operation with shift()
a=[1.,2.,3.,4.]
a += 0.5*shift(a,-1)
print,a
2.00000 3.50000 5.00000 4.50000

On Dec 21, 7:03 pm, David Fanning <n...@dfanning.com> wrote:
> samuel.le...@gmail.com writes:
>> Hello everyone, I'm trying to execute a 1-d convolution of an array,
>> signal.
>
>> Using an analytic approximation, obtaining the convolved bolometer
>> signal, bolo_signal, at time step ii, is given by the following:
>
>> nsamp=n_elements(signal)
>> const1 = exp(-tsamp/taubolo)
>> const2 = 1.-const1
>
>> bolo_signal = const2*signal
>> for ii= 1L,nsamp-1L do begin
>> bolo_signal[ii] += const1*bolo_signal[ii-1]
>> endfor
>
>> where tsamp and taubolo are scalars. Is there any way to avoid the for
>> loop in this case? The hope is to speed up the execution.
>
> I think this gives you the same results:
>
> bolo_signal += const1 * shift(bolo_signal,-1)
>
> Cheers,
>
> David
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.dfanning.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: Approximate convolution - for loop problem By: Sam on Mon, 22 December 2008 14:19
		Re: Approximate convolution - for loop problem By: Wout De Nolf on Mon, 22 December 2008 01:31
		Re: Approximate convolution - for loop problem By: David Fanning on Sun, 21 December 2008 12:44
		Re: Approximate convolution - for loop problem By: Sam on Sun, 21 December 2008 12:01
		Re: Approximate convolution - for loop problem By: David Fanning on Sun, 21 December 2008 10:03
		Re: Approximate convolution - for loop problem By: Jeremy Bailin on Tue, 23 December 2008 18:27
		Re: Approximate convolution - for loop problem By: andrews32940 on Tue, 23 December 2008 11:46

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