A is a matrix , what does this statement A([1,end],[1,end]) mean ?

The result of this command gives the 4 corners of the matrix, but can't figure out how that command works

Answer 1

[madhan ravi]

That's equivalent to:

[A(1,1), A(1,end);...
 A(1,end), A(end,end)]  

https://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html - read above linear indexing.

[Rik]

Just a note to add:

It took me a long while to realise you could not only just use addition and subtraction with end as one of the operands, but you can actually use any function:

A(randi(end),randi(end)) %select 1 point at random

[madhan ravi]

Thanks Rik!

[James Tursa]

+1 Rik, good note!

[Muhammed Thameem]

Thank you !

[Ceethal Kottakali Piyus]

Hey did you mean its equivalent to:

[A(1,1), A(1,end);...

A(end,1), A(end,end)]

or

[A(1,1), A(1,end);...

A(1,end), A(end,end)] because the second option doesn't giving the 4 corners of the matrix

[DGM]

@Ceethal Kottakali Piyus, you are correct.

A = magic(5) % an example matrix

A = 5×5

17 24 1 8 15 23 5 7 14 16 4 6 13 20 22 10 12 19 21 3 11 18 25 2 9

A([1,end],[1,end])

ans = 2×2

17 15 11 9

[A(1,1), A(1,end); A(end,1), A(end,end)]   

ans = 2×2

17 15 11 9

@RAVIKIRAN YALAMARTHI's answer may also serve as demonstration.

Answer 2

[RAVIKIRAN YALAMARTHI]

Simple example:

A = [1 2 3;4 5 6;7 8 9]
A([1,end],[1,end])

ans = 2 by 2

1 3

7 9

To call the elements in a matrix, we have to mention the row and column index values.

So, A(1,2) = 2. Since, 1st row and 2nd column element is 2.

similarly, A([1,end],[1,end]) will call the elements of,

1st row & 1st column: A(1,1)

last row & 1st column: A(end,1)

1st row & last column: A(1,end)

last row & last column: A(end,end)

[Muhammed Thameem]

Thanks, Got it 👍

[Gianpiero]

what does it mean (1:end, 1)?

[DGM]

That set of subscripts will address the first column of a matrix.

A = magic(5) % an example matrix

A = 5×5

17 24 1 8 15 23 5 7 14 16 4 6 13 20 22 10 12 19 21 3 11 18 25 2 9

A(1:end,1) % this is the same

ans = 5×1

17 23 4 10 11

A(:,1) % as this

ans = 5×1

17 23 4 10 11