Anonymous functions with 2 ou more outputs?

Hi,

I would like to know if it's possible to program an anonymous function with more than one output WITHOUT using another already defined function that have more than 1 output (I know this is actually possible). I need to program an anonymous function which takes a matriz with P+Q columns and "breaks" it in 2 matrixes: A and B, where A has P columns and B has Q columns. So the function output would be [A, B]. It'd really help me.

Thanks in advance, Guilherme

[bym]

do you really need it to be an anonymous function?

Answer 1

[Paulo Silva]

m=[1 2;3 4;5 6]
fcol=@(x)deal(x(:,1),x(:,2))
[a b]=fcol(m)

In this simple case you only got 2 columns but you can expand it to multiple columns.

m=[1 2 3 4;5 6 7 8;9 10 11 12]
fcol=@(x)deal(x(:,1:2),x(:,3:4))
[a b]=fcol(m)

[Guilherme]

What an elegant solution Sr.Paulo! Thanks a lot! =)

[Oleg Komarov]

Agree

[Paulo Silva]

You don't even need the anonymous function

m=[1 2 3 4;5 6 7 8;9 10 11 12]

[a b]=deal(m(:,1:2),m(:,3:4))

[Tobias Hübner]

Thank you for this elegant solution!!!

In combination with tables and rowfun more than helpful

Answer 2

[Oleg Komarov]

[f,g] = @(x) x+1

??? Error: Only functions can return multiple values.

If you post some code we could try to find a different solution.

Also, does this help?:

A = rand(10,10);
A = mat2cell(A,10,[5 5]);
[B,C] = A{:};

[Paulo Silva]

Oleg just use the deal function :)

[Oleg Komarov]

I never use it...

[Francois]

After many years of frustration with the fact that Matlab does not allow multiple outputs from anonymous functions, I have finally come up with a solution. It's not elegant but it works. I have created a function called mydeal.m which I put in my matlab directory

function varargout = mydeal(x)

for k = 1:length(x)

varargout{k} = x{k};

end

Now when I want an inline function with multiple outputs I just wrap a cellarray of outpus in mydeal():

Here is a simple example showing how to create an inline function that returns the a vector valued function, its gradient, and its hessian:

>> x0 = [1;1;1]; W = diag([2;4;16]);

>> f = @(x) mydeal( { 0.5*(x-x0)'*W*(x-x0), (x-x0)'*W, W } );

>> [f0,g0,H0] = f([1;2;3])

f0 =

34

g0 =

0 4 32

H0 =

2 0 0

0 4 0

0 0 16

Now if only mydeal.m could be made part of the standard matlab libraries then I could create simple inline examples in the help block of my functions that take in as input functions with multiple outputs.

[JM]

Francois, you can use deal() for that, like Paulo Silva answered:

>> x0 = [1;1;1]; W = diag([2;4;16]);

>> f = @(x) deal(0.5*(x-x0)'*W*(x-x0), (x-x0)'*W, W);

>> [f0,g0,H0] = f([1;2;3])