Default argument expression with multiple outputs

How do I get the correct output into the default argument if a function used in an expression has more than one output? E.g.

arguments
    opts.input2 (1,1) double = function_with_multiple_outputs(function_inputs)
end

Where [output1, output2, etc] = function_with_multiple_outputs(function_inputs) and function_inputs are constants or previously defined arguments. I only want, e.g. opts.input2 to be output2 from function_with_multiple_outputs.

Answer 1

[Steven Lord]

Write a local function that calls function_with_multiple_outputs with multiple outputs then returns only the one you want to use for the default value. Call that local function instead of function_with_multiple_outputs in the arguments block.

[Scott]

But arguments must appear before the first executable line of the function

[Scott]

But I should check if this works

[Scott]

I don't see how this can work because if you declare a variable it is considered an argument

[Stephen23]

"I don't see how this can work because if you declare a variable it is considered an argument"

It works for me, exactly as Steven Lord explained:

mytest(1,3)

ans = 4

function out = mytest(x,y,opts)
arguments
    x
    y
    opts.input2 (1,1) double = localfun(x,y)
end
out = opts.input2;
end
function out = localfun(varargin)
[~,out] = function_with_multiple_outputs(varargin{:});
end
function [A,B] = function_with_multiple_outputs(X,Y)
A = NaN;
B = X+Y;
end

[Scott]

Very good! Thank you.

Answer 2

[dpb]

Multiple output arguments must be unique variable names; just define the default for the specific name and it will refer to the one in that position.

[Walter Roberson]

No, you can have, for example,

[out{1:3}] = unique(randi(9, 1, 50))

out = 1×3 cell array
    {[1 2 3 4 5 6 7 8 9]}    {9×1 double}    {50×1 double}

[Scott]

I do not see this working because the outputs can have any name (different from the ones in the function declaration); it is the position that matters.

Answer 3

[Walter Roberson]

In MATLAB, there is no (useful) way to assign multiple outputs of a function to a single location, and there is no (useful) way to select a particular output from a command .

What would be legal generally in MATLAB (but not necessarily in an argument block) is

[opts.input2, opts.input2] = function_with_two_outputs();

This would assign the first output to opts.input2 and then assign the second output on top of opts.input2 .

[Stephen23]

"This would assign the first output to opts.input2 and then assign the second output on top of opts.input2 ."

Only if OPTS is scalar (or is implicitly created by that allocation).