How to find intersection of data sets

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Andrew
Andrew on 10 Jan 2014
Commented: Image Analyst on 13 Jan 2014
Hi I'm very new to Matlab and programming in general. I have two curves each represented by data sets of x,y coordinates. I want to find the point at which the two lines intersect. Obviously I could plot both sets and then find the intersection just by sight, but I want to do it mathematically.
The curves need to be evaluated by spline to be a piecewise polynomial, but after that I don't know how to solve them to find the intersection.

Answers (2)

Image Analyst
Image Analyst on 10 Jan 2014
Do you want to find the index where they are closest? What is no index matches and the crossing point is in between indexes? Do you want to find out where the cross in between indexes? So you'd have to set one cubic equal to the other in between the two indexes where it crosses.
  3 Comments
Andrew
Andrew on 13 Jan 2014
I used a combination of your suggestion of equating the cubic functions at the relevant indices and Azzi's method to find the relevant indices. It was much easier once I figured out how to dig into the spline structure. Thanks very much!

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Azzi Abdelmalek
Azzi Abdelmalek on 10 Jan 2014
Look at this example
x=0:0.01:10;
y1=sin(x);
y2=cos(x);
plot(x,y1,x,y2)
idx=sign(y2-y1)
i1=strfind(idx,[1 -1]);
i2=strfind(idx,[-1 1]);
i3=find(idx==0);
idx=unique([i1 i2 i3])
  1 Comment
Andrew
Andrew on 13 Jan 2014
Thanks very much! I used a combination of your method to find the relevant indices and Image Analyst's suggestion of equation the cubic functions at those indices.

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