How to use spline interpolation to find intersection point of two lines.

Question

PetronasAMG 2021-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/1582184-how-to-use-spline-interpolation-to-find-intersection-point-of-two-lines

评论： PetronasAMG 2021-11-9

Hi, Just new to matlab and still trying to understand spline interpolation. Although we can eye ball the interspection point, how do you use spline interpolation to find the exact interspection point? please help!

x = [-10 2];

y1 = -x

y1 = 1×2

10 -2

y2 = x+6;

plot(x,y1), hold on;

plot(x,y2);

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Answer 1

H R 2021-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/1582184-how-to-use-spline-interpolation-to-find-intersection-point-of-two-lines#answer_827119

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How about this?

clc
clear all
x = -10:1:1;
y1=-x;
y2=x+6;
%spline1
s1 = spline(x,y1);
%spline 2
s2=spline(x,y2);
% find zeros
x0 = fzero(@(x) (ppval(s1,x)-ppval(s2,x)), 0)

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PetronasAMG 2021-11-9

also is it possible to draw a red dashline from x axis to the intersection point?

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Answer 2

Matt J 2021-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/1582184-how-to-use-spline-interpolation-to-find-intersection-point-of-two-lines#answer_827259

编辑：Matt J 2021-11-9

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If they are straight lines, I'm not sure why you would want to use splines.

x = [-10 2];
y1 = -x;
y2 = x+6;
P=[x,x;y1 y2; 1 1 1 1 ];
p=cross( cross(P(:,1),P(:,2))  , cross(P(:,3),P(:,4)) );
p=p(1:2).'/p(3)  %intersection point
p = 1×2
    -3     3