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How to evaluate the x value corresponding to an y value from a plotted y(x)?

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Agent Cooper
Agent Cooper 2012-10-1
I am trying to evaluate the x value corresponding to an y value, after plotting y(x). How can I do that for any kind of values? I used the find function, but it fails. I attached the code lines below:
% parameters
mu0 = pi*4e-7;
M = 1.3e5;
R = 0.5e-6;
H = 0.67e-6;
d = [1e-6:1e-7:1e-5];
% function definition
format long;
F = (1./4)*(pi*mu0*M^2*R^4)*(1./d.^2+1./(d+2*H).^2-2./(d+H).^2);
% plot F(d)
plot(d,F,'green', 'LineWidth', 2);
% evaluating the x of an y (the d value corresponding to an F)
index = find(F == 1e-10)
d_coresp = d(index)

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回答（1 个）

Azzi Abdelmalek
Azzi Abdelmalek 2012-10-1
编辑：Azzi Abdelmalek 2012-10-1
Dont use
index = find(F == 1e-10)
use
eror=1e-11
[~,idx]=find(abs(F-1e-10)> eror
% eror depends on how many samples you are using and on the variation of F
your are not sur 1e-10 belongs to your plot
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