access outputs of functions with multiple outputs

Dear All,

I would like to find a functional way to access outputs of functions with multiple outputs. Assume I have a function "twout" defined in a m-file as follows

function [foo, bar] = twout(x, y)
 foo = x+y;
 bar = x-y;
end

I would like now to access the SECOND output "bar" from a function handle, i.e. I am looking for a function (or something which can be put into an anonymous function) called "somemagic" say, such that an anonymous function can be defined as

anoneout = @(x,y)( somemagic( twout(x, y) )

and the call

@anoneout(1,2)

produces -1.

It is clear that I can always

• write anoneout into a separate .m-file where I make a proper call to twout
• switch "foo" and "bar" in the function definition.
• return a structured data type instead of 2 outputs

My question is really whether these workaroounds are indeed the only solutions.

Thanks

gg

Answer 1

[Matt Fig]

There is a way to do it, but I am reluctant to share it because I don't think it is worthwhile to program this way. I cannot think of any reason one would want to do this, except to see if it could be done. Since I am that kind of curious person, I will show how to do it, but again I think you should go another route!

>> f = @(x,y,r) evalin('caller',[sprintf('[~,x]=twout(%.15f,%.15f);',x,y),r,'=x;'])
>> f(2,3,'r')  % Third arg is a string: [~,r] = twout(2,3)
>> r

r =

      -1

[gg]

Thanks, this definitely IS a cool way to do it. And I promise to follow your suggestion not to program it in this way, ever :-)

[Jan]

Nice, or ugly.

[Matt Fig]

Definitely ugly, and I wouldn't ever use it!

Answer 2

[Jan]

I'm not sure if I understand the question. Do you want something like this:

function Out2 = SomeMagic(Fcn, varargin)
[Out1, Out2] = feval(Fcn(vargargin{:}));
% Note: FEVAL can be omitted in modern Matlab versions

This would be called by:

z = SomeMagic(@twout, x, y);

But I do not think that this is useful, such that I assume, you are looking for something else.

[gg]

This works and is what I meant by "write anoneout into a separate .m-file where I make a proper call to twout". My question is can you do it without the additional function definition "function Out2 = ..."

Btw why do you think accessing the second output in this way is not useful?

[Jan]

I think this is not useful, because it does not add any new functionality to Matlab. The first output is still calcutate, but the command to ignore it is hidden in a function. The following would be nicer, leaner, faster and easier to debug:

[dummy, z] = twout(x, y);

Or when you do not need to write code compatible to old versions, replace "dummy" by "~".

[gg]

Sure, but this does not work if you want to call twout in an anonymous function!