Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Rafael Guerra]

You may want to study this article:
https://pdfs.semanticscholar.org/574f/8f7347a258f6431fb8316716ca51b9b7eacb.pdf

it should give you a clue or two of what you may want to implement.


-Original Message-
From: users [mailto:users-boun...@lists.scilab.org] On Behalf Of Heinz
Sent: Friday, February 09, 2018 7:44 PM
To: 'Users mailing list for Scilab' <users@lists.scilab.org>
Subject: Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB 
corrcoef function doing the job?

1   The nearest neighbour distribution of N points in a 3d-Volume with
radius R is given by
W(r) = 1 - exp[ - N (r/r)^3] and this is a Weibull distribution and not a 
Poisson distribution. The WIKI article, while correct, is a typical case where 
high level statisticians are trying to make simple things look very complicated.

2   Comparing the experimental distribution with the above prediction is
made complicated as the manufactured object has small hard spheres that push 
each other apart in the manufacturing process and the Weibull is modified 
anyway.

3   I am sill searching for a 3d spatial characterization coefficient
that differentiates between purely random arrangements and gradual regular 
arrangements.

Heinz

-Original Message-
From: users [mailto:users-boun...@lists.scilab.org] On Behalf Of Rafael Guerra
Sent: 09 February 2018 10:17
To: Users mailing list for Scilab <users@lists.scilab.org>
Subject: Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB 
corrcoef function doing the job?


Q: "I have 10,000 xyz data and want to know, if there is some regularity in 
them or if they are more or less random"
A:  look for tests of spatial randomness 
(https://en.wikipedia.org/wiki/Complete_spatial_randomness ) . If The 
experimental nearest neighbor distribution obtained previously can be compared 
to the expected Poisson distribution.


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Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Heinz]

1   The nearest neighbour distribution of N points in a 3d-Volume with
radius R is given by
W(r) = 1 - exp[ - N (r/r)^3] and this is a Weibull distribution and not a
Poisson distribution. The WIKI article, while correct, is a typical case
where high level statisticians are trying to make simple things look very
complicated.

2   Comparing the experimental distribution with the above prediction is
made complicated as the manufactured object has small hard spheres that push
each other apart in the manufacturing process and the Weibull is modified
anyway.

3   I am sill searching for a 3d spatial characterization coefficient
that differentiates between purely random arrangements and gradual regular
arrangements.

Heinz

-Original Message-
From: users [mailto:users-boun...@lists.scilab.org] On Behalf Of Rafael
Guerra
Sent: 09 February 2018 10:17
To: Users mailing list for Scilab <users@lists.scilab.org>
Subject: Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB
corrcoef function doing the job?


Q: "I have 10,000 xyz data and want to know, if there is some regularity in
them or if they are more or less random"
A:  look for tests of spatial randomness
(https://en.wikipedia.org/wiki/Complete_spatial_randomness ) . If The
experimental nearest neighbor distribution obtained previously can be
compared to the expected Poisson distribution.


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Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Stéphane Mottelet]

Hello,

There seems to be some statistical tests related to this, namely Moran’s 
or Mantel tests :


https://stats.idre.ucla.edu/other/mult-pkg/faq/general/faq-how-can-i-detectaddress-spatial-autocorrelation-in-my-data/

http://www.petrkeil.com/?p=1050

hth

S.


Le 08/02/2018 à 20:16, Heinz a écrit :

Sorry, I am lost.

I have 10,000 xyz data and want to know, if there is some regularity in them
or if they are more or less random. The concept of a mask does not come up
at all...
Best greetings
Heinz

What do you suggest should be used here?

-Original Message-
From: users [mailto:users-boun...@lists.scilab.org] On Behalf Of Samuel
Gougeon
Sent: 08 February 2018 19:19
To: Users mailing list for Scilab <users@lists.scilab.org>
Subject: Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB
corrcoef function doing the job?

Hello Heinz,

Le 07/02/2018 à 23:13, Heinz a écrit :

Friends:

I need to compute the spatial correlation coefficient of my x,y,z data in

3d.

Question 1: Is the MATLAB corrcoef function doing the job?
Question 2: How do I get corrcoef running in SciLab or C?

Do you mean the autocorrelation of a data(x,y,z) sampled distribution?
Or the intercorrelation of data(x,y,z) with a mask(x,y,z) function sampled
on the same grid?
Or anything else?

Samuel


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Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Samuel Gougeon]

Le 08/02/2018 à 20:16, Heinz a écrit :

Sorry, I am lost.

I have 10,000 xyz data and want to know, if there is some regularity in them
or if they are more or less random.


So you need and are speaking about the 3D autocorrelation of data(x,y,z).
Usually we compute it through a 3D convolution, that is easy to compute
through the FFT, noting that for an autocorrelation we just flip one of both
data array along x,y, and z before computing its FFT and going on with 
the algorithm.


Finally we use the inverse FFT to come back to the direct x,y,z space.
You may find good references on the web about the keyword 3D 
autocorrelation.


In scilab, you will mainly need

fft(A,sign,dims,incr[,option] )

since xcorr(), conv() conv2() convol2d() .. work only in 1D or 2D
(with too often duplicates to do the same thing, without "simple" 
extension to do more...)


Best regards
Samuel

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Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Heinz]

Sorry, I am lost.

I have 10,000 xyz data and want to know, if there is some regularity in them
or if they are more or less random. The concept of a mask does not come up
at all...
Best greetings
Heinz

What do you suggest should be used here?

-Original Message-
From: users [mailto:users-boun...@lists.scilab.org] On Behalf Of Samuel
Gougeon
Sent: 08 February 2018 19:19
To: Users mailing list for Scilab <users@lists.scilab.org>
Subject: Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB
corrcoef function doing the job?

Hello Heinz,

Le 07/02/2018 à 23:13, Heinz a écrit :
> Friends:
>
> I need to compute the spatial correlation coefficient of my x,y,z data in
3d.
>
> Question 1: Is the MATLAB corrcoef function doing the job?
> Question 2: How do I get corrcoef running in SciLab or C?

Do you mean the autocorrelation of a data(x,y,z) sampled distribution?
Or the intercorrelation of data(x,y,z) with a mask(x,y,z) function sampled
on the same grid?
Or anything else?

Samuel


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Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Heinz]

Thanks. While not giving me ONE number, the analysis shows that my random
generated xyz positions are uncorrelated as they should. Can one estimate
the error bars for the xy xz and yz correlations?

 

Now, I can use this approach for actual measurements in real objects.

Heinz

 

//START

function Y=corrmatrix(M)

C = cov(M);  // covariance matrix

D = sqrt(diag(C)); // standard deviations

D = inv(diag(D));

Y = D*C*D;  // correlation matrix

endfunction

n=1;

r=23;

radius = r*grand(n,1,'def').^(1/3); 

phi = 2*%pi*grand(n,1, 'def'); 

costheta = 1 - 2*grand(n,1, 'def'); 

radsintheta = radius.*sin(acos(costheta));

X = [radsintheta.*cos(phi),radsintheta.*sin(phi), radius.*costheta];

Y = corrmatrix(X)

   1.  0.0058073   0.0078778

   0.0058073   1.  0.0014375

   0.0078778   0.0014375   1.   

//END

 

From: users [mailto:users-boun...@lists.scilab.org] On Behalf Of Rafael
Guerra
Sent: 08 February 2018 18:55
To: Users mailing list for Scilab <users@lists.scilab.org>
Subject: Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB
corrcoef function doing the job?

 

Hi Heinz,

 

Scilab computes the covariance matrix and from which the correlation matrix
can be obtained using formula in
https://en.wikipedia.org/wiki/Covariance_matrix

 

Check implementation below:

 

//START OF CODE

// https://en.wikipedia.org/wiki/Covariance_matrix

function Y=corrmatrix(M)

C = cov(M);  // covariance matrix

D = sqrt(diag(C)); // standard deviations

D = inv(diag(D));

Y = D*C*D;  // correlation matrix

endfunction

 

M = grand(9,3,"def")

M(:,2) = M(:,1)*2;

Y = corrmatrix(M);

disp(M,"M")

disp(Y,"Y")

// END OF CODE

 

Regards,

Rafael

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Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Stéphane Mottelet]

Yes, a precise math formula would disambiguate the denomination.

S.

> Le 8 févr. 2018 à 19:18, Samuel Gougeon  a écrit :
> 
> Hello Heinz,
> 
>> Le 07/02/2018 à 23:13, Heinz a écrit :
>> Friends:
>> 
>> I need to compute the spatial correlation coefficient of my x,y,z data in 3d.
>> 
>> Question 1: Is the MATLAB corrcoef function doing the job?
>> Question 2: How do I get corrcoef running in SciLab or C?
> 
> Do you mean the autocorrelation of a data(x,y,z) sampled distribution?
> Or the intercorrelation of data(x,y,z) with a mask(x,y,z) function sampled on 
> the same grid?
> Or anything else?
> 
> Samuel
> 
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> users@lists.scilab.org
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Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Samuel Gougeon]

Hello Heinz,

Le 07/02/2018 à 23:13, Heinz a écrit :

Friends:

I need to compute the spatial correlation coefficient of my x,y,z data in 3d.

Question 1: Is the MATLAB corrcoef function doing the job?
Question 2: How do I get corrcoef running in SciLab or C?


Do you mean the autocorrelation of a data(x,y,z) sampled distribution?
Or the intercorrelation of data(x,y,z) with a mask(x,y,z) function 
sampled on the same grid?

Or anything else?

Samuel

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Re: [Scilab-users] spatial correlation coefficient: Is the MATLAB corrcoef function doing the job?

[Rafael Guerra]

Hi Heinz,



Scilab computes the covariance matrix and from which the correlation matrix can 
be obtained using formula in https://en.wikipedia.org/wiki/Covariance_matrix



Check implementation below:


//START OF CODE
// https://en.wikipedia.org/wiki/Covariance_matrix
function Y=corrmatrix(M)
C = cov(M);  // covariance matrix
D = sqrt(diag(C)); // standard deviations
D = inv(diag(D));
Y = D*C*D;  // correlation matrix
endfunction

M = grand(9,3,"def")
M(:,2) = M(:,1)*2;
Y = corrmatrix(M);
disp(M,"M")
disp(Y,"Y")
// END OF CODE



Regards,

Rafael
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