Matlab multiple variable assignments

Question

I would like to assign the values in a vector of length 2 to multiple variables. The output of size() is able to do this:

% works
[m,n] = size([0 0]);

However splitting this into two lines doesn't work:

sz = size([0 0]);
[m,n] = sz;
% returns:
%   ??? Too many output arguments.

What is special about the return value of size that is lost when it is assigned to a variable?

Answer 1

Matlab's output arguments are interesting this way. A function can have a variable number of outputs depending on how many the ‘user’ asked for.

When you write

[m,n] = size([0 0]);

you are requesting two output arguments. Inside the function itself this would correspond to the variable nargout equal to 2.

But when you write

sz = size([0 0]);

the size function recognises that it's a single output argument, and gives you both m and n as a vector instead of two singleton outputs. This style of behaviour is (I think) generally uncommon in Matlab.

Also note that Matlab doesn't allow multiple arguments to break up vectors:

x = [1 1]
[y,z] = x

returns Too many output arguments.

Answer 2

The custom function you introduced is quite an overkill and uses functions like eval which are considered bad practice. It can be done much shorter. That's all you need:

function [ varargout ] = split( Vector )

varargout = num2cell( Vector );

end

And because of varargout you have a variable-length output argument list and you don't need to edit your function for more argements.

It works for vectors as well as for matrices:

[a,b,c,d] = split( [1,2;3,4] )

a =  1

b =  3

c =  2

d =  4

If you don't like the matrix compatibility, include a condition and check the dimensions of the input vector.