How should I find the x value of the given y value?

Hi, I have this graph and here I would like to find the coordinates where the horizontal line and curvy graph meet together

How should I find the x-coordinate of the given y-value (this case y=6.585)?

Thank you

Answer 1

[SAA]

I am not sure if you can find an exact value since you are trying to compare 2 doubles and that's usually not a good idea, but you can get it using a tolerance.

it should be something like this:

% assuming you have 2 matrices x and y containing your data
z = x(y==6.585);  % assuming that there is an exact value that equals it but most likely you don't so you need a tolerance 
% this should work
tol = 10^-9;
z = x(abs(y-6.585) < tol); % you can also use find instead of x

Answer 2

[Star Strider]

Try something like this:

y = 6.585;
eqidx = find(diff(sign(curvy_graph - y)));
for k = 1:numel(eqidx)
    ixrng = [-1 0]+eqidx(k);
    xval(k) = interp1(curvy_graph(ixrng), x(ixrng), y);
end

That will give you the x-value for all of the intersections. Choose the ones you want to use. See the documentation on interp1 for its options.

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