Indexing a matrix with an array

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John Jönsson
John Jönsson 2020-2-23
评论： Stephen23 2020-2-23
Let's say I have a 4x4 matrix A. I can then get the item in place [2,3] by typing A(2,3).
Now let's say I have an array I=[2,3]. I would like to be able to write something like A(I) to get the same result as above. How could I do that?
Thanks.

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Stephen23
Stephen23 2020-2-23
编辑：Stephen23 2020-2-23
Use a cell array, e.g.:
C = {2,3}; % use NUM2CELL(I) if required.
A(C{:})
Tested:
>> A = rand(4,4)
A =
0.340974 0.252464 0.596849 0.800738
0.064510 0.270160 0.242550 0.518083
0.546270 0.318667 0.581832 0.409444
0.814609 0.675596 0.588558 0.353607
>> C = {2,3};
>> A(C{:})
ans = 0.24255
https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html
https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists
  2 个评论
John Jönsson
John Jönsson 2020-2-23
Thank you very much. Is there a function similar to zeros(1,n) or ones(1,n) where I can make C = {0,0,0,0,0,...} of length n? And what is C called? Do we call it a set?
Stephen23
Stephen23 2020-2-23
"Is there a function similar to zeros(1,n) or ones(1,n) where I can make C = {0,0,0,0,0,...} of length n?"
Here are two ways:
C = repmat({0},1,n)
C = num2cell(zeros(1,n))
"And what is C called?"
a cell array:
https://www.mathworks.com/help/matlab/cell-arrays.html
MATLAB does not have a "set" data type:
https://www.mathworks.com/help/matlab/matlab_prog/fundamental-matlab-classes.html

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