How do I pass a dynamic number of output variables to a function?

Some functions change their behavior dependending on the number of output variables. For example, ndgrid will create N N-Dimensional arrays where N is the number of output variables. I need to pass a number of output variables that depends on other variable (whose value is not previously known). Is it possible to do that? What is the best way to do that?

[Stephen23]

https://www.mathworks.com/help/matlab/ref/varargout.html

https://www.mathworks.com/help/matlab/ref/nargout.html

https://www.mathworks.com/matlabcentral/discussions/tips/847976-tutorial-comma-separated-lists-and-how-to-use-them

Answer 1

[Star Strider]

You can define as many outputs to a function as you want. In the call to the function, you can selectt specific outputs using the tilde (~) to suppress the outputs you do not need.

You can also use the varargout function.

Answer 2

[Steven Lord]

I need to pass a number of output variables that depends on other variable (whose value is not previously known).

I wouldn't use the word "pass" here. Nothing from the output variables enters the workspace of the function you're calling unless those variables are also specified as input arguments.

But to answer the question about how to specify output arguments when you don't know until run-time how many there will be, use a comma-separated list. See the Function Return Values section on that page for an example that calls fileparts with three output arguments. While that example hard-codes 3 output arguments, you could create that cell array C using size information computed using a variable.

S1 = callSVD(1) % 1 output

S1 = 4x1

34.0000 17.8885 4.4721 0.0000

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[U3, S3, V3] = callSVD(3) % 3 outputs

U3 = 4x4

-0.5000 0.6708 0.5000 -0.2236 -0.5000 -0.2236 -0.5000 -0.6708 -0.5000 0.2236 -0.5000 0.6708 -0.5000 -0.6708 0.5000 0.2236

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S3 = 4x4

34.0000 0 0 0 0 17.8885 0 0 0 0 4.4721 0 0 0 0 0.0000

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V3 = 4x4

-0.5000 0.5000 0.6708 -0.2236 -0.5000 -0.5000 -0.2236 -0.6708 -0.5000 -0.5000 0.2236 0.6708 -0.5000 0.5000 -0.6708 0.2236

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In fact, you could use nargout in callSVD and avoid having to pass in the number of outputs.

S1 = callSVD2 % 1 output

S1 = 4x1

34.0000 17.8885 4.4721 0.0000

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[U3, S3, V3] = callSVD2 % 3 outputs

U3 = 4x4

-0.5000 0.6708 0.5000 -0.2236 -0.5000 -0.2236 -0.5000 -0.6708 -0.5000 0.2236 -0.5000 0.6708 -0.5000 -0.6708 0.5000 0.2236

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S3 = 4x4

34.0000 0 0 0 0 17.8885 0 0 0 0 4.4721 0 0 0 0 0.0000

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V3 = 4x4

-0.5000 0.5000 0.6708 -0.2236 -0.5000 -0.5000 -0.2236 -0.6708 -0.5000 -0.5000 0.2236 0.6708 -0.5000 0.5000 -0.6708 0.2236

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function varargout = callSVD(n)
varargout = cell(1, n);
[varargout{:}] = svd(magic(4));
end

function varargout = callSVD2 % No need for n here
varargout = cell(1, nargout); % Use nargout instead
[varargout{:}] = svd(magic(4));
end

Answer 3

[Walter Roberson]

OutputVariable = cell(1,NumberOfOutputsNeeded);
[OutputVariable{:}] = FunctionCall(parameters, as, appropriate);