function chaining when one function has multiple outputs

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Simon
Simon 2024-8-19
评论： Simon 2024-8-20
Ran in:
Similar question has been asked before, but I would ask the question in a more specific manner. If the function in the input end has more than one output, there will be the error 'Not enough input arguments'. Is there a neat way to make chained function out of that situation?
f(g) % only the first output of g is kept as input for f
Not enough input arguments.

Error in solution>f (line 9)
out = x+y;
function [x, y] = g()
x = 1;
y = 2;
end
function out = f(x, y)
out = x+y;
end
Storing the outputs of the first function in two variables could be a solution, but I like to see how chaining could be done in this kind of scenario for the sake of learning.
[x, y] = g();
f(x, y)
ans = 3
  2 个评论
Stephen23
Stephen23 2024-8-20
编辑：Stephen23 2024-8-20
"Is there a neat way to make chained function out of that situation? "
No. The MATLAB apporoach is to call the two functions on two lines: this works because MATLAB's function outputs are demand driven. A discussion of why this behavior is required:
https://www.mathworks.com/matlabcentral/answers/344486-generate-comma-separated-list-in-single-line-of-code#comment_461351
Simon
Simon 2024-8-20
Thanks for the very clear explanation. It's worth of keeping the max(max) example in mind.

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采纳的回答

Steven Lord
Steven Lord 2024-8-19
Ran in:
Suppose you had a function that could be called with either 1 output or more outputs, and a function that can accept 1 input or multiple inputs. If you chained those two so that the output(s) of the first of those functions were passed into the second function, how should MATLAB know with how many outputs to call the first function? To give an example (not necessarily a realistic example but just to illustrate the situation):
A = magic(4);
L = lu(A);
oneOutputCase = max(L)
oneOutputCase = 1x4
16.0000 13.5000 14.2500 13.0000
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[L, U] = lu(A);
twoOutputCase = max(L, U)
twoOutputCase = 4x4
16.0000 2.0000 3.0000 13.0000 0.3125 13.5000 14.2500 0 0.5625 0.4352 1.0000 5.6667 0.2500 1.0000 0 0.0000
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chainCase = max(lu(A))
chainCase = 1x4
16.0000 13.5000 14.2500 13.0000
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Were you expecting the twoOutputCase output from the chainCase call? The lu function can return up to five outputs (though the fourth and fifth are only supported for sparse inputs, but the first three are supported for both sparse and full inputs) and the max function can accept (as data inputs) one or two inputs. How would you expect MATLAB to distinguish between those two cases?
  1 个评论
Simon
Simon 2024-8-20
I see what the interpreting machine behind Matlab might see from your example. A human mathematician has the leisure to 'boldly' use symbols like max(min) or min(max) because he has tacit context to rely on.

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