need to calculate autocorrelation radius of a matrix

[chaski]

Working with a n x n matrix of non-negative real values, I'm trying to calculate a 2d analog of 'autocorrelation length' -- that is, I want to find the minimum euclidean (or similar) distance at which, on average, two entries in the matrix (separated by that critical distance) will show a mutual correlation of less than 1/e (or 1/2, or some other such 'natural' threshold).  

Analogous 'correlation radius' measures are used as metrics of landscape 'ruggedness' or 'roughness', I think, but I've looked in vain for an established method to calculate them. Does anyone know of a script that could (perhaps with tweaking at my novice level) be used to do so?

Thanks.

[Matt Foster-6]

On Wed, Jun 18, 2008 at 12:05 AM, chaski <pearsonn@...> wrote:

>
> Working with a n x n matrix of non-negative real values, I'm trying to
> calculate a 2d analog of 'autocorrelation length' -- that is, I want to find
> the minimum euclidean (or similar) distance at which, on average, two
> entries in the matrix (separated by that critical distance) will show a
> mutual correlation of less than 1/e (or 1/2, or some other such 'natural'
> threshold).
>
> Analogous measures are used as metrics of landscape 'ruggedness' or
> 'roughness', I think, but I've looked in vain for an established method to
> calculate them. Does anyone know of a script that could (perhaps with
> tweaking at my novice level) be used to do so?
>

I did a quick google, and found this:
http://scien.stanford.edu/class/psych221/projects/00/jichien/matlab/AutoCorr2.m
Which you might be able to adapt to your needs.

I've also attached a couple of functions that I wrote a while ago, and
which might be useful.
I've not ever used them in anger, but the algorithm is from a
textbook, and they give the same results as the example in the book.

Cheers,

Matt
--
Matt Foster | http://my-mili.eu/matt



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