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Convolution, IDL & Numerical Recipes [message #32678]

Thu, 31 October 2002 12:50

aceves
Messages: 4
Registered: October 2002

Junior Member

Hello..

I am using IDL for some of my research and have a particular problem
with convolution of two arrays. I have used IDL's CONVOL procedure
and subroutine CONVLV given in NUMERICAL RECEIPES..both give
different results. I hope some one can shed light on what the
reason might be.

Thank you. Hector

*********
Problem:
*********

At the IDL prompt I entered and obtained:
----------

IDL> a=[0,0,0,0,0,1,1,1,1,1,0,0,0,0,0,0] ; signal!
IDL> k=[1,0,0,0,0,0,0,0,0] ; kernel!
IDL> z=convol(a,k)
IDL> print, z
0 0 0 0 0 0 0 0
0 1 1 1 0 0 0 0

With Numerical Receipes (Example Book in Fortran, Program XCONVLV, Chap.13)
----------------------

The Signal file, or Data is (ibin,DATA)

1 0.
2 0.
3 0.
4 0.
5 0.
6 1.
7 1.
8 1.
9 1.
10 1.
11 0.
12 0.
13 0.
14 0.
15 0.
16 0.

The Kernel or Response Function is (jbin,RESPNS=KERNEL) ..an identity filter

1 1.
2 0.
3 0.
4 0.
5 0.
6 0.
7 0.
8 0.
9 0.

The Fortran program gives (ibin,Convolution,Expected value):

I CONVLV Expected

1 0.000000 0.000000
2 0.000000 0.000000
3 0.000000 0.000000
4 0.000000 0.000000
5 0.000000 0.000000
6 1.000000 1.000000
7 1.000000 1.000000
8 1.000000 1.000000
9 1.000000 1.000000
10 1.000000 1.000000
11 0.000000 0.000000
12 0.000000 0.000000
13 0.000000 0.000000
14 0.000000 0.000000
15 0.000000 0.000000
16 0.000000 0.000000

-----
As shown, the results given by the numerical subroutine from NR
gives the expected results and differ from the one by IDL's CONVOL.

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[Message index]

		Convolution, IDL & Numerical Recipes By: aceves on Thu, 31 October 2002 12:50
		Re: Convolution, IDL & Numerical Recipes By: aceves on Wed, 06 November 2002 17:02
		Re: Convolution, IDL & Numerical Recipes By: JD Smith on Tue, 05 November 2002 14:42
		Re: Convolution, IDL & Numerical Recipes By: R.G. Stockwell on Tue, 05 November 2002 05:34
		Re: Convolution, IDL & Numerical Recipes By: David Fanning on Fri, 01 November 2002 12:14
		Re: Convolution, IDL & Numerical Recipes By: David Fanning on Fri, 01 November 2002 11:12
		Re: Convolution, IDL & Numerical Recipes By: muzic on Tue, 12 November 2002 06:10
		Re: Convolution, IDL & Numerical Recipes By: muzic on Tue, 12 November 2002 06:10
		Re: Convolution, IDL & Numerical Recipes By: R.G. Stockwell on Fri, 01 November 2002 10:44

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