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

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Diaa
Diaa on 27 Nov 2020
Commented: Walter Roberson on 23 Jun 2021
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.

Accepted Answer

Walter Roberson
Walter Roberson on 27 Nov 2020
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
  6 Comments
Walter Roberson
Walter Roberson on 23 Jun 2021
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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