'deal' doesn't distribute the elements of a calculated array out of cellfun

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Diaa 2020-11-27

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/664158-deal-doesn-t-distribute-the-elements-of-a-calculated-array-out-of-cellfun

评论： Walter Roberson 2021-6-23

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

For the following

syms syma symb 
eqns = [...
    syma*exp(symb)== 1,...
    syma*exp(symb*1500) == 5,...
    ];
vars = [syma symb ];
[sola, solb ] = deal(cellfun(@(C) double(C),struct2cell(vpasolve(eqns,vars)),'UniformOutput',true)')

the ouput is

sola = 0.9989 0.0011

and

solb = 0.9989 0.0011

while, expectedly, sola should take only the first value 0.9989 and solb should take inly the second value 0.0011.

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Walter Roberson 2020-11-27

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https://ww2.mathworks.cn/matlabcentral/answers/664158-deal-doesn-t-distribute-the-elements-of-a-calculated-array-out-of-cellfun#answer_557313

在 MATLAB Online 中打开

deal has never done that for any kind of variable.

You are calculating a single vector in the cellfun, so your code with deal() comes down to:

[A,B] = deal([9 11])
A = 1×2
     9    11
B = 1×2
     9    11

deal() has two functions:

%assign the same value to multiple variables
[A, B] = deal(9)
A = 9
B = 9
%historic. split multiple outputs between multiple variables:
C = num2cell([9 11]);
[A, B] = deal(C{:})
A = 9
B = 11
%these days you can do that without the deal() call:
C = num2cell([10 12]);
[A, B] = C{:}
A = 10
B = 12

Neither of those modes splits a vector into multiple output variables.

Expand = @(C) C{:};
Split = @(V) Expand(num2cell(V));
[A, B] = Split([11 13])
A = 11
B = 13

The amount of thought needed to get the correct solution using subsref() far exceeds any execution time you might hypothetically gain by using subsref() for this purpose. The subsref version is hard to maintain. And requires two helper function calls (to num2cell and to substruct)

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