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Editorial Team
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Asked: 2026-05-24T08:19:54+00:00

Here is the graph I currently have : The Dotted Blue line represented the

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Here is the graph I currently have
:

The Dotted Blue line represented the y value that corresponds to the x value I am looking for. I am trying to find the x values of the line's intersections with the blue curve(Upper)

The Dotted Blue line represented the y value that corresponds to the x value I am looking for. I am trying to find the x values of the line’s intersections with the blue curve(Upper).Since the interesections do not fall on a point that has already been defined, we need to interpolate a point that falls onto the Upper plot.

Here is the information I have:

LineValue – The y value of the intersection and the value of the dotted line( y = LineValue)
Frequency – an array containing the x value coordinates seen on this plot. The interpolated values of Frequency that corresponds to LineValue are what we are looking for
Upper/Lower – arrays containing the y value info for this graph

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1 Answer

  1. Editorial Team

    Example solution using FZERO:

    %# data resembling your curve
x = linspace(-100,100,100);
f = @(x) 1-2.*exp(-0.5*x.^2./20)./(2*pi) + randn(size(x))*0.002;
VALUE = 0.8;

%# solve f(x)=VALUE
z1 = fzero(@(x)f(x)-VALUE, -10);  %# find solution near x=-10
z2 = fzero(@(x)f(x)-VALUE, 10);   %# find solution near x=+10

%# plot
plot(x,f(x),'b.-'), hold on
plot(z1, VALUE, 'go', z2, VALUE, 'go')
line(xlim(), [VALUE VALUE], 'Color',[0.4 0.4 0.4], 'LineStyle',':')
hold off

    screenshot

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