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# Adding outlier to a matrix

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Niki on 22 May 2014
Commented: Star Strider on 22 May 2014
Hi , I have a matrix of intensities (n*p). I want to add an outlier to it. Do you have any idea about how to simulate an outlier? I was thinking to take the mean of matrix and then multiply it to some very high value?
Do you have any idea ?

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### Accepted Answer

Star Strider on 22 May 2014
I suggest:
M = rand(4,5); % Create data
Msts = [mean(M(:)) std(M(:))];
Outlier = Msts(1)+5*Msts(2);
Define the outlier by a multiple of the standard deviation from the mean. An value of 5*std is quite far out.

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Star Strider on 22 May 2014
See if this does what you want:
load('example.mat')
OutsXR = mean(X,2) + 5*std(X,[],2);
figure(1)
plot([X OutsXR])
Niki on 22 May 2014
Not that one but this one helps
OutsXR = mean(X,1) + 5*std(X,[],1);
however, I accept your answer Thanks
Star Strider on 22 May 2014
My pleasure, and thanks!

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### More Answers (1)

Roger Wohlwend on 22 May 2014
Actually you answered your question yourself. Instead of the mean I would use the maximum value of the matrix. Multiply that number by a certain value. That's all. It is quite easy.

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Niki on 22 May 2014
In fact, I want to know whether it is scientifically correct or not? It is not a number. As I explained it is a matrix of n*p so I wont have a value as outlier but a row which corresponds as an outlier
On the other hand, do you know any way to show it as a outlier ?

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