# How do I find the instersection on my plot?

2 views (last 30 days)
Agnese Chini on 11 Oct 2021
Edited: Matt J on 11 Oct 2021
I have a plot with the errorbar. The data coming from a matrix 21x6 and the errorbar from another matrix. I need to find where (for a given y-axis value) the functions intersect the curves and at what coordinate. Since the values of the graph are given by a matrix, only the y axis correspond to the physical values, for the x axis I changed the values via
xticks([1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21])
xticklabels({'-20','-18','-16', '-14', '-12', '-10', '-8', '-6','-4','-2','0','2', '4', '6', '8', '10', '12', '14', '16', '18', '20'})
The graph is this one:

Matt J on 11 Oct 2021
Edited: Matt J on 11 Oct 2021
You can use fzero, e.g.,
fun=@(x)x^2;
y=4;
x_intersect=fzero(@(x) fun(x)-y,[0,1e6])
x_intersect = 2.0000
Matt J on 11 Oct 2021
Edited: Matt J on 11 Oct 2021
The ydata is not a particular column. The column as I told you before are the different line
Yes, the ydata in my original example also represented one particular line, but as I told you you can loop over your matrix columns and apply my technique to each.
xdata=-20:2:20
for i=1:6
ydata=Matrix(:,i);
y=...
fun=griddedInterpolant(xdata,ydata,'linear'); %interpolator
x_intersect(i) = fzero(@(x) fun(x)-y,[0,1e6])
end

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