# how to mark and print the intersecting coordinates of two lines

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Anitha Limann on 9 Oct 2021
Commented: Star Strider on 10 Oct 2021
I have x1,y1 and x2, y2 data sets that give me two lines graphs.
I want to find the intersecting point of these two lines and and print it on the graph.
I tried following different functions like intesect but did not work.
##### 2 CommentsShowHide 1 older comment
Anitha Limann on 10 Oct 2021
Yes. i have these datasets
x1=[10,20,30,40,50,75,100,125,150,175,200,225,250,275];
t1=[1.6,3.2,4.8,6.4,8,12,16,20,24,28,32,36,40,44];
x2=[150,175,200,225,250,275,300,325,350,375,400];
t2=[26.62,29.69,32.75,35.82,38.89,41.96,45.02,48.09,51.16,54.23,57.29];
some point values. where i get this graph
so i want to find this intersecting point and print it on the graph.

Star Strider on 10 Oct 2021
Much depends on what ‘x1’, ‘y1’ and the rest are.
One approach (sssuming multiple intersections, although thiis will also work for only one intersection) would be —
x1 = linspace(-2, 15);
y1 = 2 + 3*x1;
x2 = linspace(-10, 10);
y2 = (x2-2).^2;
xq = linspace(min([x1,x2],[],2), max([x1,x2],[],2)); % Create Common 'x' Vector
y1q = interp1(x1, y1, xq, 'pchip','extrap'); % Interpolate To It
y2q = interp1(x2, y2, xq, 'pchip','extrap'); % Interpolate To It
idx = find(diff(sign(y1q-y2q))); % Approximate Indices Of Intersections
for k = 1:numel(idx)
idxrng = max(1,idx(k)-2) : min(numel(xq),idx(k)+2); % Index Range
xi(k) = interp1(y1q(idxrng)-y2q(idxrng), xq(idxrng), 0); % Interpolate X-Intersection
yi(k) = interp1(xq(idxrng), y1q(idxrng), xi(k)); % Interpolate Y-Intersection (Either Y-Vector Will Work)
end
Intercepts = [xi; yi]
Intercepts = 2×2
0.3001 6.7004 2.9004 22.1012
figure
plot(x1, y1)
hold on
plot(x2, y2)
plot(xi, yi, '+r', 'MarkerSize',10)
hold off
grid
legend('y1','y2','Intersections', 'Location','best')
Experiment to get the desired result.
.
##### 2 CommentsShowHide 1 older comment
Star Strider on 10 Oct 2021
As always, my pleasure!
.

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