how to call out single element in matrix

thank you very much for ur help Prof./Dr./Sir...but, can u explain a little bit what is the meaning of 1:2 and the 2: 2 in the bracket here sir A(1:2:end) + A(2:2:end)

Walter Roberson 2022-7-29

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MATLAB has an operator that it calls "colon" that is available in two forms.

A:B

means the sequence of values starting from A, and add one each time, ending with the last number that is not greater than B. So for example 2.1:4 would be 2.1 then 3.1 and then when it internally looked at 4.1 it would be greater than the 4 endpoint so that sequence would stop with just the two values.

A:B:C

is closely related. If B is positive then you start from A, add B each step, and end before exceeding C. If B is negative such as 5:-1:3 then you add B each step (so you are subtracting) but you end when the result would be less than C, so 5:-1:3 would be 5 4 3

1:2:end thus means starting at 1 and add 2 each time, so 1 3 5 and so on. The "end" in A(1:2:end) stands in for the maximum index for that array. With A being 6 long A(1:2:end) would be A(1:2:6) which would be A([1 3 5]) . A(2:2:end) with length 6 would be A(2:2:6) or A([2 4 6])

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