Nested For Loops help

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Ife M
Ife M 2018-2-25
回答： Fahad HCT2021 2020-4-5
Hello!
I am attempting to use a nested for loop on two columns of data. Here's an example of what I am trying to accomplish
A = [1;2;3;4]
B = [4;3;2;1]
for i = 1:numel(A)
for j = 1: numel(B)
diff = A(i) - B(j)
end
end
I want the output to be [(1-4) (2-4) (3-4) (4-4) (1-3) (2-3) (3-3) (4-3) etc] where it iterates through the A matrix completely but selects the same value from the B matrix each time. Essentially: A(1)-B(1), A(2)-B(1), A(3)-B(1), A(4)-B(1) and have an output matrix that contains all of the iteration outputs. So it should be a 16x1 matrix Any advice on what I am doing wrong?
  1 个评论
Stephen23
Stephen23 2018-2-26
编辑：Stephen23 2018-2-26
DO NOT use diff as a variable name!
Because then the inbuilt (and very useful) function diff will not work!
Always check if a variable name is used:
which diff

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采纳的回答

David Fletcher
David Fletcher 2018-2-25
You're not retaining the variable 'diff' but just keep replacing it with the latest subtraction. You could initialize diff=[] before the loops and then change the assignment to diff=[diff A(i)-B(j)]. Computationally, it's not great, but it should do the job.

更多回答（1 个）

Fahad HCT2021
Fahad HCT2021 2020-4-5
% Define variables
syms ;
f=@(i) ;
% Loop to create vector df1
for i= ;
deriv=diff( ); % Find the general ith derivative of f
df1(i)=subs( ); % Substitute x=1
end; % DO NOT CHANGE CODE ON THIS LINE
df1 % Display the vector df1

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