Want to find and use a corresponding y-value for a given x-value

I'm trying to find the value of y when x is at half max - i.e. when x = 50, what does y equal? I then need to use that y-value in further calculations, so I need to assign it a name or have it returned somehow. The lists of numbers I will be using goes from x=0 to 100 in about 600+ steps and 50 is not in the same location in every data set, so none of the help in the interpolation/max/median type areas has been helpful so far, I don't know what keywords to use to get successful search in MATLAB help. (I think this is probably simple however I am a new user so thanks for the help)

Answer 1

[Sean de Wolski]

%Sample x/y
x = linspace(0,100,572);
y = 2.*x.^2-31*x;

%Index of x closest to 50 and corresponding y
[junk, idx50] = min(abs(x-50));
y50 = y(idx50);

NOTE: This isn't interpolating, just extracting the closest value to 50. Do you need an interpolation to 50 exactly?

[Matt Fig]

Megan says,

No, the closest value is actually better as some are 49.9 etc.

[Matt Fig]

Sean de says,

The above works then.

Welcome to MATLAB Answers!

[Megan]

thank you :)