how can I add zeros elements to a matrix?

I have a matrix a: a= [1 2 3; 1 2 3; 1 2 3] I want to add zero rows and cols and convert it to b:

 b=

     1     2     3     0     0 
     1     2     3     0     0
     1     2     3     0     0
     0     0     0     0     0
     0     0     0     0     0
how is it possible?
(size of 'a' can be different, in fact it's a matrix which shows image m*n)

Answer 1

[Salaheddin Hosseinzadeh]

Hi Moein,

there are different ways to do this. One of which is to define a fully zero matrix with all zeros

newMatrix = zeros(5,5); % all zero matrix

Then assign the non zero elements.

newMatrix(1:3,1:3) = oldMatrix; % oldMatrix is a, newMatrix is b

This is one way to do it.

Another way would be to concatenate the oldMatrix with zeros.

neMatrix_1 = [oldMatrix,zeros(3,2)];  % horizontal concatenation
newMatrix_2 = [newMatrix_1;zeros(2,5)]; % vertical concatenation

This should give you the same in newMatrix_2

[moein Pakdel sefidi]

thanks Salaheddin.

Answer 2

[Andrei Bobrov]

a= [1 2 3; 1 2 3; 1 2 3] 
b = a
b(5,5) = 0

Answer 3

[Ugur Aygun]

Hi Moein,

Easiest way to do this is to use padarray command.

a= [1 2 3; 1 2 3; 1 2 3];
padarray(a,[2,2],0,'post')

ans =

       1     2     3     0     0
       1     2     3     0     0
       1     2     3     0     0
       0     0     0     0     0
       0     0     0     0     0

Here [2,2] indicates how many terms you will add to rows and columns respectively.

[David Buzzell]

This requires the Image Processing Toolbox