Passing a function as a parameter in a MATLAB function [duplicate] - function

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Closed 10 years ago.
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Passing a function as argument to another function
Below is a simple code for the bisection method. I would like to know how to be able to pass in any function I choose as a parameter instead of hard coding functions.
% This is an implementation of the bisection method
% for a solution to f(x) = 0 over an interval [a,b] where f(a) and f(b)
% Input: endpoints (a,b),Tolerance(TOL), Max # of iterations (No).
% Output: Value p or error message.
function bjsect(a,b,TOL,No)
% Step 0
if f(a)*f(b)>0
disp('Function fails condition of f(a),f(b) w/opposite sign'\n);
return
end
% Step 1
i = 1;
FA = f(a);
% Step 2
while i <= No
% Step 3
p = a +(b - a)/2;
FP = f(p);
% Step 4
if FP == 0 || (b - a)/2 < TOL
disp(p);
return
end
% Step 5
i = i + 1;
% Step 6
if FA*FP > 0
a = p;
else
b = p;
end
% Step 7
if i > No
disp('Method failed after No iterations\n');
return
end
end
end
% Hard coded test function
function y = f(x)
y = x - 2*sin(x);
end
I know this is an important concept so any help is greatly appreciated.

Answer 1

The simplest method is using anonymous functions. In your example, you would define your anonymous function outside bjsect using:
MyAnonFunc = #(x) (x - 2 * sin(x));
You can now pass MyAnonFunc into bjsect as an argument. It has the object type of function handle, which can be validated using isa. Inside bjsect simply use MyAnonFunc as if it is a function, ie: MyAnonFunc(SomeInputValue).
Note, you can of course wrap any function you've written in an anonymous function, ie:
MyAnonFunc2 = #(x) (SomeOtherCustomFunction(x, OtherInputArgs));
is perfectly valid.
EDIT: Oops, just realized this is almost certainly a duplicate of another question - thanks H. Muster, I'll flag it.