How to estimate the Gaussain kernel based on spatial bandwidth for KDE

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Tania 2014-11-21

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编辑： Tania 2014-11-21

Hi,

I want to use bandwidth h= 10 to estimate Gaussian Kernel

Not sure how to use it for each point

please advice

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Image Analyst 2014-11-21

What does "bandwidth" mean in this context? It usually refers to the width of a range of frequencies in a spectral (Fourier) domain. Do you mean the spatial width of the Gaussian in the spatial domain?

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Answer 1

the cyclist 2014-11-21

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If you have the Statistics Toolbox, you can use the ksdensity function for this, and set the bandwidth as a parameter.

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Tania 2014-11-21

编辑：Tania 2014-11-21

Is it possible to use it in a loop (without the toolbox)?

Not sure how to do this.

Any advice will be appreciated.

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Answer 2

the cyclist 2014-11-21

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I suggest you take a look at kde in the MATLAB File Exchange.

Even if this function does not help you directly, it may give you some hints at how to code what you need yourself.

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the cyclist 2014-11-21

编辑：the cyclist 2014-11-21

@tania:

The kde function I mentioned in this answer is not the ksdensity function supplied by MATLAB itself. It is a user-contributed function at the File Exchange that seems to do much of what you want to do.

I am going to say something that might sound a bit harsh. Sorry.

It seems that you don't know a lot about kernel density estimation, and you also don't know a lot about MATLAB. I am not confident we can really teach you both of these things in this forum.

The kde file is very well documented code that does much of what you need. If at all possible, you need to study that, and maybe you need to find someone locally who understands MATLAB really well, or kernel density estimation really well, to help you understand what that code is doing.

Tania 2014-11-21

I am totally new to this. Will follow your advice. ty

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Answer 3

Image Analyst 2014-11-21

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Lacking a clear definition of bandwidth, I'm going to hurl out a SWAG: how about if you use the fspecial() function to create a Gaussian? It will create a small array where the window width in elements, and the standard deviations (width within the window) is what you specify.

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Tania 2014-11-21

编辑：Tania 2014-11-21

在 MATLAB Online 中打开

Let me explain again.

 Mean shift is a procedure for locating the maxima of a density function given discrete data sampled from that function. It is useful for detecting the modes of this density.This is an iterative method, and we start with an initial estimate x . Let a kernel function K(x_i - x) be given. This function determines the weight of nearby points for re-estimation of the mean. Typically a Gaussian kernel on the distance to the current estimate is used, K(x_i - x) = e^{-c||x_i - x||^2} .

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