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

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PetronasAMG on 9 Nov 2021
Commented: PetronasAMG on 9 Nov 2021
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);

H H on 9 Nov 2021
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)
PetronasAMG on 9 Nov 2021
also is it possible to draw a red dashline from x axis to the intersection point?

Matt J on 9 Nov 2021
Edited: Matt J on 9 Nov 2021
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

R2021b

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