Talk:Positive-definite function

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[edit] I'm confused

There seems to be confusion about positive semi-definite versus positive definite. Sam Coskey 03:02, 6 December 2006 (UTC)

[edit] Too narrow

The explanation of positive definite function seems to be too narrow here.

In general a positive definite function is any function f(x,y) with the property that all finite index sets lead to positive definite matrices. Not, as the article says, just ones of the form f(x-y). Those of the form f(x-y) are called "stationary" or "homogeneous".

Also this is in the category "complex analysis" which I think may be too limiting. The value of the function doesn't necessarily have to be complex to have the property of positive definiteness.

For a reference see, e.g., Matthias Seeger, "Gaussian Processes for Machine Learning".

Baxissimo 06:58, 18 January 2007 (UTC)Baxissimo

[edit] Bochner's theorem?

I don't quite understand -- were you looking for a reference to Bochner's theorem? Why slap on a "fact" tag? Is this a particularly controversial statement or are you just seeking aid in finding a reference?

If you simply want aid finding a source, how about [1], [2], [3], or [4]. Also, if you simply want aid in finding a source, just ask on the talk page; there's no need to mark up the article. Lunch 15:39, 27 March 2007 (UTC)