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Can somebody explain me this answer?

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a=[1 2; 3 4]; a(3*ones(2)) ans= 2 2 2 2

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Accepted Answer

madhan ravi
madhan ravi on 9 Sep 2019
The code copies the third element of a as 2 by 2 matrix, see the below example:
>> a
a =
1 2
3 4
>> a(:)
ans =
1
3
2
4
>> a([3,3;3,3])
ans =
2 2
2 2
>>

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More Answers (3)

James Tursa
James Tursa on 9 Sep 2019
Edited: James Tursa on 9 Sep 2019
You are using linear indexing into "a". This matrix:
>> 3*ones(2)
ans =
3 3
3 3
When used as indexing, it means "create a 2x2 matrix result, and put the 3rd element of "a" into that matrix result at each spot". Since the 3rd element of "a" in memory is the value 2, you get a 2x2 matrix of all 2's as your answer.

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Bob Nbob
Bob Nbob on 9 Sep 2019
a=[1 2; 3 4]; % Dictates a matrix, 'a,' and it values. Is a 2x2 matrix
a(3*ones(2)) % Calls the elements of 'a' which are located at 3*a 2x2 matrix of ones.
ans= 2 2 2 2 % This answer is returned because a(3) is the element in the first row, second column, a 2, and all four elements of the ones matrix will call the same element of 'a.'

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Marko Kosijer
Marko Kosijer on 9 Sep 2019
thank you so much guys!

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