meaning of the notation of accessing the elements of the 2D matrix using 4 subscripts?

Recently, I saw that some people use four sub-scripts to access the elements of a 2D matrix! For eg,If A=[1,2,3,4 ; 5,6,7,8 ; 9,10,11,12 ; 13,14,15,16], then the command, A(1,2,1,1) yields me an answer of 2.

How? What's the meaning of this command? Thanks in advance!!

[Jan]

Writing A(1,2,1,1) is valid, but simply confusing and misleading for the reader.

[Stephen23]

"How? What's the meaning of this command?"

All arrays implicitly have infinite trailing singleton dimensions. You can easily check this yourself:

>> size(A,3)
ans =  1
>> size(A,4)
ans =  1
>> size(A,99)
ans =  1
>> size(A,999)
ans =  1
>> size(A,9999)
ans =  1

Answer 1

[MUHAMMED IRFAN]

For a 2d Matrix, A(1,2,1,1) is equivalent to A(1,2).

Consider it as A(dimension1,dim2,dim3,dim4). As it is a 2d matrix, the value of dim3,dim4,dim5... will be 1.

ie, A(1,2,1,1,1,1,1,1,1,1) will also give you the value 2 !!

[Jan]

+1. Exactly. In Matlab singleton trailing dimensions are ignored.

x = zeros(2,3,1)
size(x)     % [2, 3]
size(x, 9)  % 1