Duplicate a matrix using nested for loops

Question

Tyler M 2018-2-20

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/383621-duplicate-a-matrix-using-nested-for-loops

评论： Stephen23 2018-2-20

In Matlab I have been trying to duplicate matrix A [2,4,1;6,7,2;3,5,9] to matrix B using nested for loops. I know the general format uses an algorithm within the loop ie.

 m=3
 n=3
 b=zeros(m,n)
 for i=1:m
 for j=1:n
 B(m,n)= *algorithm here*
 end
 end

I can not find an algorithm that would work for this matrix and I believe that it was designed this way on purpose. I have tried pulling numbers out of matrix A using

A=[2,4,1;6,7,2;3,5,9]
for c=A(1,:)
for d=A(2,:)
for e=A(3,:)
end
end
end
B=[c;d;e]

but this just assigns the values for the last column of A to a 1x3 matrix B (B=[1;2;9]

I have also tried scouring the www for help with how to duplicated a matrix that is not algorithmic using nested for loops to no avail.

Any help or guidance would be much appreciated.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Stephen23 2018-2-20

???

Why not just avoid the pointless loops and use B=A ?

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Roger Stafford 2018-2-20

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/383621-duplicate-a-matrix-using-nested-for-loops#answer_305987

在 MATLAB Online 中打开

What's wrong with

B = A; % ?

However, if you absolutely must do it with nested for-loops then do:

[m,n] = size(A);
B = zeros(m,n);
for i1 = 1:m
  for i2 = 1:n
    B(i1,i2) = A(i1,i2);
  end
end
_

3 个评论
显示 1更早的评论隐藏 1更早的评论

Roger Stafford 2018-2-20

编辑：Roger Stafford 2018-2-20

You wouldn't want to use just B=A inside those for-loops. That would be extremely wasteful of computing time. B=A by itself does the job without for-loops. Using for-loops with B(i1,i2) = A(i1,i2); is bad enough.

Tyler M 2018-2-20