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

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André Bueno
André Bueno 2024-7-18
评论： Stephen23 2024-7-19
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?

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回答（2 个）

Steven Lord
Steven Lord 2024-7-18
Ran in:
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
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
S3 = 4x4
34.0000 0 0 0 0 17.8885 0 0 0 0 4.4721 0 0 0 0 0.0000
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
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
Walter Roberson
Walter Roberson 2024-7-18
OutputVariable = cell(1,NumberOfOutputsNeeded);
[OutputVariable{:}] = FunctionCall(parameters, as, appropriate);

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