find intersection points of a line and a curve.

I am attaching here the plot. I want to get the intersection points of the horizontal red line with the curve. Also, I want to draw the vertical lines from these intersection points. How both of these tasks can be done? In case, question is not clear feel free to comment.

Answer 1

[Adam Danz]

There are several ways to get the x values at each intersection of the y-value. The simplest solution is to use the intersections() function from the file exchange (I show a similar demo in this answer, "method #2").

That function will return the (x,y) coordinates of the intersection points. Use the x values to plot vertical lines using xline().

% x is a vector of x-values at each intersection
arrayfun(@xline,x)

Or, if you're more comfortable with for-loops,

for i = 1:numel(x)
    xline(x(i))
end

[NAVNEET NAYAN]

In your demo of "method #2", X1 and Y1 must be of same size. My X1 is a scalar and it is single whereas Y1 is of length 282 . Is there any way for this?

[Adam Danz]

> In your demo of "method #2", X1 and Y1 must be of same size

Correct. In any demo that would be the case. (x,y) coordinates come in pairs so they must have the same number of elements.

> My X1 is a scalar and it is single whereas Y1 is of length 282

Unless I've misunderstood your question, I think you have this reversed. The horizontal line is defined by at least two x values (the end points) and 1 unique y-value which is repeated for each x value.

The horizontal line in your plot might be something like X1=[1, 280]; Y1 =[15, 15];

[NAVNEET NAYAN]

Yes you are correct. I had reversed. Thank you for solving the query and explaining it too.