How can I nest a function in a function?

Question

Barbaros Teoman Kosoglu 2022-10-13

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https://ww2.mathworks.cn/matlabcentral/answers/1824933-how-can-i-nest-a-function-in-a-function

评论： John D'Errico 2022-10-13

function AD = AD(n)
    A = zeros(n);
    for i=1:n
        for j=1:n
            A(i,j) = 1/(i+j-1);
        end
    end
    Ainv = A\eye(n);
    Eye = eye(n);
    AD = Eye-Ainv*A;
end
function A = hilbert(n)
    A = zeros(n);
    for i=1:n
        for j=1:n
            A(i,j) = 1/(i+j-1);
        end
    end
end

I want to nest hilbert function in AD function, since hilbert is actually in AD. But I am getting "Unrecognized function or variable 'A'" error. What can I do here?

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Answer 1

Fangjun Jiang 2022-10-13

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在 MATLAB Online 中打开

MyAD=AD(3)
MyAD = 3×3
1.0e-13 *

         0         0    0.0089
   -0.0711         0         0
    0.1421    0.0711    0.0711
function AD = AD(n)
A = hilbert(n);
Ainv = A\eye(n);
Eye = eye(n);
AD = Eye-Ainv*A;
end
function A = hilbert(n)
A = zeros(n);
for i=1:n
    for j=1:n
        A(i,j) = 1/(i+j-1);
    end
end
end

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Barbaros Teoman Kosoglu 2022-10-13

Thank you.

Fangjun Jiang 2022-10-13

To be clear, hilbert(n) here is a 'local function'. There is no need to make it a 'nested function' based on its content.

See documents for their differences.

I think 'local function' is more suitable in this case.

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Answer 2

John D'Errico 2022-10-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1824933-how-can-i-nest-a-function-in-a-function#answer_1073558

编辑：John D'Errico 2022-10-13

在 MATLAB Online 中打开

See that I wrote hilbert differently. Feel free to use doubly nested loops there. But why?

As well, NEVER name a function the same thing as a variable in that function!!!!!!!!! NEVER. NEVER. Having said that three times, it must be true. You named the function AD, then returned a variable named AD. A BAD idea.

ComputeAd(5)
ans = 5×5
1.0e-11 *

    0.0171         0   -0.0071   -0.0099   -0.0099
    0.0909    0.0455    0.1592    0.1137    0.1137
   -0.3638   -0.3638   -0.1819   -0.1819   -0.3638
    0.7276    0.3638    0.3638    0.3638    0.5457
   -0.1819   -0.0909   -0.0909   -0.1819   -0.2728

It works.

function AD = ComputeAd(n)
  A = hilbert(n);
  Ainv = A\eye(n);
  Eye = eye(n);
  AD = Eye-Ainv*A;
  
  function A = hilbert(n)
    [i,j] = meshgrid(1:n);
    A = 1./(i+j-1);
  end
end