Creating a column vector for each variable in a for loop?

Question

Bob 2014-12-13

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https://ww2.mathworks.cn/matlabcentral/answers/166534-creating-a-column-vector-for-each-variable-in-a-for-loop

评论： Christof Omar 2017-12-20

Here is my code:

D=[1 4 7 5];
for i=1:length(D)
    A=D(1,i)
    B=A+3
    C=B-5
end

How do I create a column vector of values for each variable in the for loop (I want a column vector for all the A values, another column vector for all the B values, and one last column vector for all the C values?

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Answer 1

Guillaume 2014-12-13

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You would just index into the destination variables in the for loop, the same way you index into the origin vector. Optionally, you would also predeclare the outputs:

D=[1 4 7 5];
A = zeros(numel(D), 1);
B = zeros(numel(D), 1);
C = zeros(numel(D), 1);
for i = 1 : numel(D)
  A(i, 1) = D(i); %or simply A(i) = D(i), if A is predeclared
  B(i) = A(i) + 3;
  C(i) = B(i) - 5;
end

However, for arithmetic operations like that, you shouldn't use a for loop and just operate on the whole vector at once. Since you start with a row vector and want columns vector, at some point you need to transpose the result: