matrix indexing and manipulation
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Hi
(Newbie question)
I have a matrix which is Z=131x47 If I do ZA=Z(1:end); am I right in thinking the elements are rearragned columnwise? Say for example I am interested in the element ZA(1,3000), how do I know what the position of this value is in the original matrix Z?
Thanks
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Yoav Livneh
2011-7-26
You can use ind2sub.
[rowIndex, colIndex] = ind2sub(size(Z),Index);
I think this should work.
更多回答（2 个）
Image Analyst
2011-7-26
0 个投票
You could use numel() to tell how many elements are in your Z matrix, then check if 3000 <= numel(Z).
Andreas Goser
2011-7-26
First, you are correct that this code would arrange elements columnwise. You may have a look at the RESHAPE command for a more general way of reshaping a matrix. Using REHSHAPE or your code however, does not preserve the size of the orginal matrix. You need to store that to be able to invert the reshape.
You may also be interested to know that matrices in MATLAB can be accessed as vectors
X=rand(10,7);
X(5,4)=1 % Setting to one to spot it better
X(35) % element 4*7+5
Maybe there is a way to write your code without creating an additional vector ZA,
2 个评论
dia-2011
2011-7-26
Andreas Goser
2011-7-26
OK, the answer above WRT IND2SUB seems to meet your needs. My additional point was that you may be able to avoid the "conversion".
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