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Hey everyone,

I have the following case : (picture linked to the tocpic).

Let's suppose that i have two points with their value on y-axis equals to -20.5 and -19.5. I also know their value on x-axis (let's suppose 10^9 and 2*10^9). I don't have more points between them.

I would like to know : How can I find the value on X-axis of the point that have the value on y-axis equal to -20.

If it's not understandable, I hope the picture linked to it will be helpful !

Thanks you very much !

Star Strider
on 15 Sep 2021

Example —

x = linspace(0, 50);

y = 30*(1-exp(-0.1*x));

f = @(x) 30*(1-exp(-0.1*x));

x_20 = interp1(y, x, 20) % From Data

f_20 = fzero(@(x) f(x)-20, rand) % From Function

figure

plot(x, y)

grid

hold on

plot(x_20, 20, '+r')

plot(f_20, 20, 'xg')

hold off

.

KSSV
on 15 Sep 2021

Read about interp1. If you have curve data as (x,y), at the point xi you can seek the value using:

yi = interp1(x,y,xi)

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