I have a function "f" that returns a 1x2 vector, and I need to make a 3x2 matrix M by stacking the outputs f(x1), f(x2), f(x3) on top of each other, but Matlab won't parse it.

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Joe Exotic 2021-10-31

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https://ww2.mathworks.cn/matlabcentral/answers/1575848-i-have-a-function-f-that-returns-a-1x2-vector-and-i-need-to-make-a-3x2-matrix-m-by-stacking-the-o

评论： Joe Exotic 2021-10-31

采纳的回答： dpb

在 MATLAB Online 中打开

First, I wrote:

M = [f(x1); f(x2); f(x3)]

That didn't work - it gave me only the first outputs of every f (resulting in a 3x1 matrix). Then, I tried

M = zeros(3,2) + [f(x1); f(x2); f(x3)]

which gave me the same thing copied into two columns. Then, I typed

[M1 M2] = [f(x1); f(x2); f(x3)]

which gave me a "too many outputs" error. I tried some other variations of a similar thing in one to two lines, but nothing really worked. Of course I could fix this particular issue with some slightly longer solution (3+ lines of code) but that would be clumsy and not versatile to other dimensions. What is the simplest and most useful way around this issue?

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Answer 1

dpb 2021-10-31

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https://ww2.mathworks.cn/matlabcentral/answers/1575848-i-have-a-function-f-that-returns-a-1x2-vector-and-i-need-to-make-a-3x2-matrix-m-by-stacking-the-o#answer_820743

在 MATLAB Online 中打开

The first syntax will work if the function actually returns a vector --

>> x=rand(1,5);
>> fnX=@(i)x(i:i+1);
>> fnX(1)
ans =
          0.58          0.95
>> M=[fnX(1);fnX(2);fnX(3)]
M =
          0.58          0.95
          0.95          0.25
          0.25          0.24
>> x
x =
          0.58          0.95          0.25          0.24          0.71
>> 