Finding intersection of curve and a line

Hello! I apologize if that has been asked before - I tried finding an answer but I didn't really understand any of them/many of them didn't work because it wasn't for this situation specifically.

I have this graph (see below), with two y lines on them. I was hoping to find the coordinate intersection of the bottom line (let's call it secondY) and the exponential curve (which we can call curve). I would then like to draw an x line wherever the intersection x value is. What would be the simplest way to do this?

I appreciate your help, thank you!

Answer 1

[Star Strider]

Your ‘curve’ has noise between x=0 and x=200 or so. You will likely need to exclude that region.

One option is to use interp1, for example:

xq = interp1(curve(idxrng), x(idxrng), lineval);

where ‘idxrng’ are the index values that exclude the noise, and ‘lineval’ is whatever y-value the line has.

Another option is to use polyfit to approximate the exponentially-descending part of the curve:

p = polyfit(x(idxrng), y(idxrng), 3);
xq = roots(p - lineval);

Without your data, it is not possible to write specific code.