When writing user defined functions how can i have a function of a variable as an input variable?

I am trying to write a function for example: function res = MyFunction(x1,x2,x3,f)

where f is a function of x but Matlab doesn't seem to like this. Is there a way around this without previously defining a function?

[Steven Lord]

Can you show a little more context, like how you define the variables x1, x2, x3, and f with which you call MyFunction and what exactly "Matlab[sic] doesn't seem to like this" means?

1. Does it throw an error, and if so what is the full text of the error message?
2. Does it issue a warning, and if so what is the full text of the warning message?
3. Does it return a result different than what you expect?
4. Does it do something else (and if so, what does it do?)

[Jacob Carias]

I'm trying to solve f(x)=0 using a process that uses an iteration. So I have initial values, say 'x1,x2,x3', and I want f to be a generic function of x(i). I use these initial values and f(initial values) to calculate x(4),x(5) and so on. but when I use my function; function res = Myfunction(x1,x2,x3,f) and sub in cos(x) for f Matlab returns Undefined function or variable'x'.

I understand why this happens because x isn't defined but I don't know how to get past this.

For a better example:

I have:

function res = ITERATION(f,x0,x1,n)

% where f is a function

x(2) = x1 + f(x1) + f(x0);

x(3) = x2 + f(x2) + f(x1);

for i = 4:n

x(i) = x(i-1) + f(x(i-1)) + f(x(i-2));

end

for i = 2:n

res(i) = (x(i))^2

end

purely as an example

when I run the new function and sub a function of 'x' it returns 'x' is undefined

Answer 1

[Steven Lord]

If you're doing something like:

res = ITERATION(cos(x),x0,x1,n)

that will not work. MATLAB will try to evaluate the expression cos(x) and pass the result into ITERATION as the first input. But x may not be defined, and it's certainly not going to do what you want based on the way ITERATION is written. Instead pass a function handle into ITERATION as the first input argument.

res = ITERATION(@cos, x0, x1, n)

If instead the function were f(x) = x+1, use an anonymous function:

res = ITERATION(@(x) x+1, x0, x1, n)

[Jacob Carias]

Thank you very much