Array Indexing, Array within an Array

I need help understanding how this code works.

Consider the variables B = [1 5 8] and D = [1; 1; 1]. When I write the code B(D,:) I am getting the output of [1 5 8; 1 5 8; 1 5 8] and I am not sure why.

Please be thorough in your explination.

Thanks for the help.

Answer 1

[Matt J]

Because, by definition,

 B(D,:) = [   B(D(1),:)   ;  B(D(2),:) ; B(D(3),:) ]
     
        = [   B(1,:)   ;  B(1,:) ; B(1,:) ]
        
        = [1 5 8; 1 5 8; 1 5 8]