Plot a point of intersection between 2 lines or curves

Hi,

If I have a case where x = [1 2 3 4 5] and y1=[2 4 6 8 10] and y2=[4.2 5 5.8 6.1 7.2], and I plot(x,y1) and plot(x,y2) how do I plot the point of intersection. There is a possibility that these two lines dont actually intersect as I came up with the problem on the spot. But, I want a simplified version of how I can plot the point of intersection so I can hover over it and get the co-ordinates.

Thanks.

Answer 1

[Star Strider]

Try this:

x  = [1 2 3 4 5];
y1 = [2 4 6 8 10];
y2 = [4.2 5 5.8 6.1 7.2];

x_int = interp1(y1-y2, x, 0);                       % X-Intersection Coordinate
y_int = interp1(x, y1, x_int);                      % Y-Intersection Coordinate


figure
plot(x, y1)
hold on
plot(x, y2)
plot(x_int, y_int, 'sr')
hold off
grid

The coordinates themselves are (x_int,y_int).

[Mayowa Milburn]

Thanks man, really helpful. It makes sense that its an interpolation rather than using polyfit & polyval.

[Star Strider]

As always, my pleasure!

Interpolation is the best option in most instances, however if there are more than one intersection, they need to be calculated separately. That is relatively straightforward to do, the only additional step is that the interpolations require a loop to calculate them separately.