How to add a first row and a first column of zeros in a matrix?

hi,

i have a matrix, for example

A=[1 2 3; 4 5 6; 7 8 9]

A = 3×3

1 2 3 4 5 6 7 8 9

how can i add a first row of zeros and a first colum of zeros to reach the following results?

B=[0 0 0 0; 0 1 2 3; 0 4 5 6; 0 7 8 9]

B = 4×4

0 0 0 0 0 1 2 3 0 4 5 6 0 7 8 9

and how can i delete the last row and the last column of a matrix to reach this second results?

C=[0 0 0; 0 1 2; 0 4 5]

C = 3×3

0 0 0 0 1 2 0 4 5

thank you very much matlab users!

Answer 1

[Arif Hoq]

A=[1 2 3; 4 5 6; 7 8 9];
AA=[zeros(1,3);A];
AAA=zeros(4,1);
B=[AAA AA];
B(:,end)=[];
B(end,:)=[]

B = 3×3

0 0 0 0 1 2 0 4 5

Answer 2

[Star Strider]

The easiest way is to create an appropriate zeros matrix and just index into it —

A=[1 2 3; 4 5 6; 7 8 9];
B = zeros(size(A,1)+1,size(A,2)+1);
B(2:end,2:end) = A

B = 4×4

0 0 0 0 0 1 2 3 0 4 5 6 0 7 8 9

C = B(1:end-1,1:end-1)

C = 3×3

0 0 0 0 1 2 0 4 5

Four lines of code to do everything!

.

Answer 3

[Simon Dengler]

bit more general and faster?

A=[1 2 3; 4 5 6; 7 8 9];

A = 3×3

1 2 3 4 5 6 7 8 9

B=zeros(size(A)+1);
B(2:end,2:end)=A

B = 4×4

0 0 0 0 0 1 2 3 0 4 5 6 0 7 8 9