How to get matlab to find a point on a graph where there is a sudden change?
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Joe Smith
on 5 Mar 2015
Commented: Image Analyst
on 5 Mar 2015
I have a graph of 'data point number' against 'distance'.
Around data point number 2500 damage is introduced and the graph has a sudden spike.
Is there some way of getting matlab to detect this sudden change?
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Accepted Answer
Michael Haderlein
on 5 Mar 2015
You can define a threshold value either for y or for diff(y). Assume you define failure as point when y>0.2:
plot(x,y), hold all
ind=find(y>0.2,1,'first');
plot(x(ind:end),y(ind:end),'rx')
fprintf(1,'Failure at x = %d\n',ind);
If you want to define the threshold on diff(y), do the same but use ind=find(diff(y)>0.2,1,'first'); instead.
2 Comments
Image Analyst
on 5 Mar 2015
%d means to print the value of ind assuming that ind is an integer. \n adds a line feed (new line) after it's been printed.
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