intersection between a many plots and a line

Hello!

Im been looking and cant find a definitive soltion to how to find the intersection between a yline and multiple plots

between the plots and the yline i need to find the intersecting points but I cant seem to find out how to do it.

any help would be great thanks!

figure(1)       % Q4
plot(SNR,PERSF7,'-or','MarkerSize', 8,'LineWidth',2)

hold on
plot(SNR,PERSF8,'-*','MarkerSize', 8,'LineWidth',2)
plot(SNR,PERSF9,'-diamond','MarkerSize', 8,'LineWidth',2)
plot(SNR,PERSF10,'-x','MarkerSize', 8,'LineWidth',2)
plot(SNR,PERSF11,'-^','MarkerSize', 8,'LineWidth',2)
plot(SNR,PERSF12,'-square','MarkerSize', 8,'LineWidth',2)
% 5% point
yline(0.05)
hold off
xlim([-25 0])
ylim([0 1])

Answer 1

[Walter Roberson]

There is no built-in facility to take the intersection between yline or xline, with anything.

You are looking for the places where (PERSF7 - 0.05) touches or crosses 0, (PERSF8 - 0.05) touches or crosses 0, and so on.

rng(655321)
PERSF7 = randn(1,50) / 5;
SNR = (1:numel(PERSF7))/10;

target_y = 0.05;
plot(SNR, PERSF7);
yline(target_y);

locs = find((PERSF7(1:end-1)-target_y) .* (PERSF7(2:end) - target_y) <= 0);
locs

locs = 1×20

3 5 6 9 11 12 16 17 22 23 24 25 31 32 34 36 41 42 48 49

This says that there is a zero crossing between PERSF7(3) and PERSF7(4), between PERSF7(5) and PERSF7(6), between PERSF7(6) and PERSF7(7), between PERSF7(9) and PERSF7(10) and so on.

for k = 1 : numel(locs)
    SNR_crossing(k) = interp1(PERSF7(locs(k):locs(k)+1), SNR(locs(k):locs(k)+1), target_y);
end

figure();
plot(SNR, PERSF7);
hold on
plot(SNR_crossing, target_y .* ones(size(SNR_crossing)), 'r*');
hold off

Answer 2

[Matt J]

You could use linexlines2D from this FEX download,

https://www.mathworks.com/matlabcentral/fileexchange/93470-intersections-of-multiple-2d-lines-or-line-segments

rng(655321)
PERSF7 = randn(1,50) / 5;
SNR = (1:numel(PERSF7))/10;
target_y = 0.05;


XY=[SNR;PERSF7];
[XYout, map]=linexlines2D(XY(:,1:end-1),XY(:,2:end), [0,1,-target_y]);

plot(SNR, PERSF7, XYout(1,:), XYout(2,:),'rx');
yline(target_y);