access outputs of functions with multiple outputs

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gg
gg 2012-9-6
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

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采纳的回答

Matt Fig
Matt Fig 2012-9-6
编辑：Matt Fig 2012-9-6
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
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Jan
Jan 2012-9-6
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.
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Jan
Jan 2012-9-6
编辑：Jan 2012-9-6
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
gg 2012-9-6
Sure, but this does not work if you want to call twout in an anonymous function!

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