Passing in a function as an argument

Dear all,

I would like to write a Function M-file f.m, which is to contain a primary function called f as well as two subfunctions called subFunc1 and subFunc2, respectively.

Within the primary function f, I need to call subFunc1; what is the proper syntax for passing subFunc2 as an input parameter to such a call of subFunc1?

Any feedback would be very much appreciated.

Regards, Kaloyan

Answer 1

[Ted Shultz]

you use the "@" character to pass a function, not the output of a funcitn. This looks like this:

function main
clc
testCode(@sum, [1 2 3])       % calls "testCode" with builtin matlab function "sum"
testCode(@doubleSum, [1 2 3]) % calls "testCode" with custom function defined below
end

function valOut = testCode(funcIn, numIn)
% funcIn is a function passed to this function! you call as you would the passed function:
valOut = funcIn(numIn);
end

function ds = doubleSum(numIn)
ds = 2*sum(numIn);
end

[Abdul Hanan Wali]

and what if we have to compare them. like if ds == valOut it should return true

[Steven Lord]

Comparing functions or function handles is unlikely to be what you want.

Now comparing the results of evaluating a function or function handle, on the other hand, is often useful.

f1 = @sin;
f2 = @(x) cos(pi/2-x);
x = [0 pi 2*pi];
norm(f1(x)-f2(x)) < 1e-6 % Don't use == for floating point comparison

ans = logical
   1

Note that directly trying to compare f1 and f2 won't work.

f1 == f2 % error

Operator '==' is not supported for operands of type 'function_handle'.

Answer 2

[Stuart Kozola]

To pass in a function to another function, use function handles (@).

sf2 = @(inputs) subFcn2(inputs)

then call it in subFcn1 as

out1 = subFcn1(sf2)

or alternatively

out2 = subFcn1(@subFcn)

Note that you add @ to the function name to declare it as a function (vs. a variable) to be passed into the function.

Now if you have constant parameters that need to be passed into subFcn1, you can define the sf2 as

sf2 = @(input) subFcn(input,param1,param2)

and to call sf2 it only takes in input

out2 = sf2(input)

Note that the constant parameters are already included in the definition of sf2 which only takes in one input.

If you need more explaination or examples, look at the doc:

http://www.mathworks.com/help/matlab/matlab_prog/overview-1.html

Answer 3

[Azzi Abdelmalek]

a=@subFunc2

Then call your function with a argument

[Kaloyan Marinov]

Do you mean I should pass subFunc2 as an input parameter to a call of subFunc1 it as follows:

a = @subFunc2;

subFunc1(a);

?

Answer 4

[Omkar Dumne]

How does matlab help help in passing function arguments