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How to generate a function from x-y vectors?

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Ajay Goyal
Ajay Goyal on 6 Feb 2017
Edited: Luca on 31 Mar 2020
Hello MATLAB users. I got two vectors (say x and y). Is there any way to create a function i.e. y=f(x). I do not want the expression. I just want to create the function in matlab for further calculations. For ease: x=[1 5 0 32 8]; y=[10 1 654 32 100];

  2 Comments

the cyclist
the cyclist on 6 Feb 2017
Your question is not clear. What does "use these vectors in function form" mean?
Do you mean you want to find a function f(x) that will (approximately?) fit the x-y data? If so, what type of function? A polynomial?
Ajay Goyal
Ajay Goyal on 6 Feb 2017
If I do not get expression; its ok. I just want to create a funtion from these vectors so that further calculations like Fourier series etc can be done

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Accepted Answer

Nicolas Schmit
Nicolas Schmit on 4 Sep 2017
You question is not very clear, so I will try to guess what you are trying to do.
If you want to define a purely symbolic function f(x), use the following syntax.
syms f(x)
If you want to create a function from data points x and y, use the griddedInterpolant function to create a interpolation of x and y.
x=[1 5 0 32 8];
y=[10 1 654 32 100];
[~, index] = sort(x);
F = griddedInterpolant(x(index), y(index));

More Answers (3)

Yifan Ma
Yifan Ma on 6 Feb 2018
What you are looking for is map container. https://de.mathworks.com/help/matlab/ref/containers.map-class.html

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Luca
Luca on 31 Mar 2020
Edited: Luca on 31 Mar 2020
Hi,
I have 2 vector (x, y) and I desire math expression y=f(x)
x must be syms. How to?
tnks

  2 Comments

Ajay Goyal
Ajay Goyal on 31 Mar 2020
Hi,
As much I did understood your query, you wish to establish relation as y=f(x) and values of x are not known. To answer, I believe, it is not possible as the values of x and y is the first necessity to develop a function. Then only you may use it to predict y for input values of x.
Contrary, if you just want to define a function, you may do it following way:
%%%%Main File:
syms x
[ y ] = Untitled2( x )
%%%%Function file:
function [ y ] = Untitled2( x ) %%%%same name as in main file. Func. file will be stored with this name
y=x.^2; %%%%wrtite the function. Say
end
Kindly let me know, if your query has been resolved.
Best Luck
Ajay
Ajay Goyal
Ajay Goyal on 31 Mar 2020
both files has to be in the working folder

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Luca
Luca on 31 Mar 2020
Edited: Luca on 31 Mar 2020
For you.

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