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Re: what is the dist function's mean? [message #43739 is a reply to message #43549]

Fri, 22 April 2005 14:07

Benjamin Hornberger is currently offline

Benjamin Hornberger
Messages: 258
Registered: March 2004

Senior Member

lixiaoyao wrote:
> Is there anybody who can explain the dist for me?
> I know dist(100) generate a 100X100 matrix,but what is the value for
> it
> come from? In the help file,they said it is the frequency,but I do not
> understand.
> also,what is the purpose for this function?
> Thanks a lot
>

Maybe we should admit that the manual doesn't do a good job of
explaining this function.

Dist will always return a 2-d array. "Frequency" is meant in the context
of Fourier Transforms (and maybe others). If you F.T. a 2-d array, you
can use DIST() to create an array with the spatial frequencies
corresponding to the F.T. array. The division into quadrants comes from
the way the FFT() function arranges its result. Check the help entry for
FFT for more information.

If you SHIFT() the result of DIST() by (n/2, n/2), you get an array
where each pixel value is equal to the distance from the center. This is
useful to create arrays with circular symmetry (like circular apertures).

Benjamin

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[Message index]

		what is the dist function's mean? By: lixiaoyao on Fri, 22 April 2005 10:31
		Re: what is the dist function's mean? By: Benjamin Hornberger on Sat, 23 April 2005 11:55
		Re: what is the dist function's mean? By: lixiaoyao on Sat, 23 April 2005 10:36
		Re: what is the dist function's mean? By: Benjamin Hornberger on Sat, 23 April 2005 10:16
		Re: what is the dist function's mean? By: Benjamin Hornberger on Wed, 18 May 2005 11:57
		Re: what is the dist function's mean? By: lixiaoyao on Sat, 23 April 2005 08:01
		Re: what is the dist function's mean? By: David Fanning on Sat, 23 April 2005 07:19
		Re: what is the dist function's mean? By: lixiaoyao on Sat, 23 April 2005 07:16
		Re: what is the dist function's mean? By: Benjamin Hornberger on Fri, 22 April 2005 14:07
		Re: what is the dist function's mean? By: David Fanning on Fri, 22 April 2005 13:39
		Re: what is the dist function's mean? By: K. Bowman on Fri, 22 April 2005 13:05
		Re: what is the dist function's mean? By: Dick Jackson on Fri, 22 April 2005 12:36
		Re: what is the dist function's mean? By: David Fanning on Fri, 22 April 2005 12:24
		Re: what is the dist function's mean? By: Haje Korth on Fri, 22 April 2005 11:43

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