I want to make a recursive formula and execute two statements with the same variables at the same time

Question

Jelle Bosschaart 2020-10-11

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评论： Rena Berman 2020-10-13

clc
clear all
a=1
b=0
while irrelevant
    b = [a]                  % The answer I want from this statement is b = [1]
    a = [a b]                % The answer I want from this statement is [1 0] , I dont want to use calculated b (from the statement before) but b=0 ('the first b').
end
% I dont want to really want to make b0,b1,b2,b3 because this needs to become recursive with an 'while' and 'for' statement.
% So I really want to execute b = [a] and a = [a b] at the same time; but I cannot figure out how to fix this.

ADDON:

Thank you for your suggestion.

Although it doesn't really work for our problem.

We'd like the following to be recursive:

...  etc ...
clc
clear all
a1=1
b1=0
b2=[a1]
a2=[a1 b1]
b3=[a2]
a3=[a2 b2]
b4=[a3]
a4=[a3 b3]
... etc ...

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Rik 2020-10-12

Please don't remove substantial parts of your question. It vastly reduces the usefulness of the answers to future readers.

Rena Berman 2020-10-13

(Answers Dev) Restored edit

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Answer 1

Walter Roberson 2020-10-11

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NO.

You cannot do what you want in MATLAB.

At the moment, I cannot think of any programming language that supports what you are asking for.

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Answer 2

Alan Stevens 2020-10-11

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What about a temporary variable for b:

...
    bt = b;
    b = [a];
    a = [a bt];
...

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Walter Roberson 2020-10-11

http://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

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Answer 3

Steven Lord 2020-10-12

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Use a cell array (or two cell arrays, though b is a copy of most of a.)

a = {1};
b = {0};
cellToFill = 2;
while cellToFill < 20
    b{cellToFill} = a{cellToFill-1};
    a{cellToFill} = [a{cellToFill-1}, b{cellToFill-1}];
    cellToFill = cellToFill + 1;
end

Instead of referring to numbered variables, refer to cells in a and b.

a{4}
b{5}

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Steven Lord 2020-10-12

So you need all permutations of 8 ones and 4 zeros? That's a very different question than the one you asked.

If that's not the full question please state exactly what you're trying to do. In particular, what restrictions are there (if any) about where the 1's can be placed.

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Answer 4

Alan Stevens 2020-10-12

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I'm obviously not understanding something here (not unusual!),. Doesn't the following do what you want:

a = 1;
b= 0;
n = 5;
[a, b] = recur(a,b,n);
disp('Recursive')
disp(a)
disp(b)
% Compare with
a1 = 1; b1 = 0;
b2 = a1; a2 = [a1 b1];
b3 = a2; a3 = [a2 b2];
b4 = a3; a4 = [a3 b3];
b5 = a4; a5 = [a4 b4];
b6 = a5; a6 = [a5 b5];
disp('Incremental')
disp(a6)
disp(b6)
function [a, b] = recur(a,b,n)
          if n>1
              bt = b;
              b =  a;
              a = [a bt];
              n = n-1;
              [a, b] = recur(a,b,n);
          else
              bt = b;
              b = a;
              a = [a bt];
          end
  
end