Convert input of a function from scalar to vector

I am implementing Newton-Raphson method to find a zero.

I would like to convert this function:

F =@(x, y) x - y;

To that function:

F =@(X) X(1) - X(2);

Here I wrote it with x and y, but I have actually any amount of scalars (typically 800 or more). How do I automate the process?

[Cris LaPierre]

Do you mean x and y are vectors containing 800 numbers?

A scalar is a vector of size 1x1, so you'd have to have 800 unique variables to have 800 scalars.

[Lukas-Marie Jean Stanislas Gamard]

Yes, I meant x and y scalars, as I figured it to be my base case.

In my application I actually want to transform

F =@(x1, ..., x200, y1, ..., y200, z1, ..., z200, t1, ..., t200)

into

F =@(XY, ZT)

where both XY and ZT are 400x1 vectors (want column vectors for matrix multiplication)

Answer 1

[Walter Roberson]

A lot of the time, the easiest way to convert a function to accept vector inputs instead of individual inputs, is to use the Symbolic toolbox, and use matlabFunction() with the 'vars' option, and pass in a cell array of the variables to be grouped together. For example,

syms x y
F = x - y

F = 

fun = matlabFunction(F, 'vars', {[x, y]})

fun = function_handle with value:
    @(in1)in1(:,1)-in1(:,2)

[Lukas-Marie Jean Stanislas Gamard]

Thanks!

This was actually exactly what I wrote except for the {} wrapping the symbolic vetor in matlabFunction(). Did not spot it when I read the documentation.

[Walter Roberson]

The {} turns out to be important! And it is definitely easy to overlook or not understand the significance of it the first (numerous) times reading the matlabFunction documentation.

Answer 2

[Cris LaPierre]

The main difference between the two functions you show is how the data is passed in.

F([x,y]) is the same as F(X) when X is a vector.

[Lukas-Marie Jean Stanislas Gamard]

Yes, that is why I wrote it F(x,y), without [ ].

[Cris LaPierre]

You need the [] to pass in x and y as a single input X.

F =@(X) X(1) - X(2);
x=5;
y=1;
F([x,y])

ans = 4

Answer 3

[Ashwini]

F =@(X) X(1) - X(2); x=5; y=1; F([x,y])