Populating matrix with coordinates of each element

Question

Will Pihir 2021-8-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1442259-populating-matrix-with-coordinates-of-each-element

评论： DGM 2021-8-31

Hi Guys,

I am trying to populate a 100x100 matrix so that the first element is assigned to 1 and the last element is assigned to 100.

Any suggestions? I've already create the specified matrix using zeros and ones but I am guessing I have to use a nested for-loop with the outer looping over the rows and the inner looping over the columns to reassign each element?

Any assistance would be much appreciated.

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Will Pihir 2021-8-30

Yeah I just figured it out as I was typing.

Oops.

Same premise still applies

Matt J 2021-8-30

Same premise still applies

Then, you should respond to the answer that you have been given by @DGM. Accept-click the answer if it does what you want and describe what is missing if it does not.

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Answer 1

DGM 2021-8-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1442259-populating-matrix-with-coordinates-of-each-element#answer_776394

编辑：DGM 2021-8-29

在 MATLAB Online 中打开

For your example using row-wise linear indexing:

s = [5 10]; % output size
reshape(1:prod(s),s(2),s(1)).'
ans = 5×10
     1     2     3     4     5     6     7     8     9    10
    11    12    13    14    15    16    17    18    19    20
    21    22    23    24    25    26    27    28    29    30
    31    32    33    34    35    36    37    38    39    40
    41    42    43    44    45    46    47    48    49    50

Obviously, you'd change s to suit your needs. To do the same thing columnwise:

s = [5 10]; % output size
reshape(1:prod(s),s(1),s(2))
ans = 5×10
     1     6    11    16    21    26    31    36    41    46
     2     7    12    17    22    27    32    37    42    47
     3     8    13    18    23    28    33    38    43    48
     4     9    14    19    24    29    34    39    44    49
     5    10    15    20    25    30    35    40    45    50

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Will Pihir 2021-8-31

Thanks for the answer DGM. This was exactly what I was looking for.

Just so I can understand it better, what does the syntax .' at the end of the row-wise linear indexing code do?

DGM 2021-8-31

在 MATLAB Online 中打开

.' transposes the array. For a 2D array, t's the same as doing

Atranspose = permute(A,[2 1]);

Since reshape() fills the result along columns, and the requirements need the indices ordered along rows, I have reshape generate the transpose of the desired array (hence the dimension order swap).

s = [5 10]; % output size
result = reshape(1:prod(s),s(2),s(1)) % with no transpose
result = 10×5
  11    21    31    41
  12    22    32    42
  13    23    33    43
  14    24    34    44
  15    25    35    45
  16    26    36    46
  17    27    37    47
  18    28    38    48
  19    29    39    49
  20    30    40    50

Transposing gives the correct orientation.

result = result.'
result = 5×10
   2     3     4     5     6     7     8     9    10
  12    13    14    15    16    17    18    19    20
  22    23    24    25    26    27    28    29    30
  32    33    34    35    36    37    38    39    40
  42    43    44    45    46    47    48    49    50

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