create a matrix from matrix with zeros elements

I have a matrix obtained

A=[ 1 2 3 4;5 6 7 8;9 10 11 12; 13 14 15 16];

So I just would like to obtain another matrix but with some indexs (or elements ) and the rest is zeros

So I need the output matrix to be

O=[ 1 2 0 0 ;2 1 0 0 ;0 0 6 8;0 0 8 16]

So can anyone advise me with the best way ?

Thanks,

[Sindar]

what is the logic of which elements are zero, and what value the non-zero ones take?

[Ali Tawfik]

Hi Sindar,

Thanks for your prompt reply.

Well ,I try to explain you more,

I had already a matrix, and I wanna create a new matrix based on matrix obtained earlier, then assign zeros in the matrix with some elements from the first matrix,

For example:

x=[1 2 3 4 5 6 ;

7 8 9 10 11 12;

13 14 15 16 17 18;

19 20 21 22 23 24;

25 26 27 28 29 30;

31 32 33 34 35 36]

Then, I wanna create Y as the following:

Y=[x(1,1) x(1,4) 0 0;

x(1,4) x(4,4) 0 0;

0 0 x(3,3) x(6,3);

0 0 x(6,3) x(6,6)]

I created zeros(4) so I have the new matrix, my question is how to assign some elements to the new matrix to create Y ???

Thanks,

Answer 1

[Spencer Chen]

You can create a new matrix of the same size:

B = zeros(size(A));

Then assign non-zero data in B.

Blessings,

Spencer

[Ali Tawfik]

Hi Spencer,

Thanks for your prompt reply.

I meant, I had already a matrix, and I wanna create a new matrix based on matrix obtained earlier, then assign zeros in the matrix with some elements from the first matrix,

For example:

x=[1 2 3 4 5 6 ;

7 8 9 10 11 12;

13 14 15 16 17 18;

19 20 21 22 23 24;

25 26 27 28 29 30;

31 32 33 34 35 36]

Then, I wanna create Y as the following:

Y=[x(1,1) x(1,4) 0 0;

x(1,4) x(4,4) 0 0;

0 0 x(3,3) x(6,3);

0 0 x(6,3) x(6,6)]

I created zeros(4) so I have the new matrix, my question is how to assign some elements to the new matrix to create Y ???

Thanks,

Answer 2

[Sindar]

I still don't quite see the pattern, but you can insert elements manually:

x=[1 2 3 4 5 6 ;
      7 8 9 10 11 12;
     13 14 15 16 17 18;
     19 20 21 22 23 24;
    25 26 27 28 29 30;
    31 32 33 34 35 36];

Y = zeros(4);
Y(1,1) = x(1,1);
Y(1,2) = x(1,4);
Y(2,1) = x(1,4);
Y(2,2) = x(4,4);
Y(3,3) = x(3,3);
Y(3,4) = x(6,3);
Y(4,3) = x(6,3);
Y(4,4) = x(6,6);

% or
Y = zeros(4);
Y(1:2,1:2) = [x(1,1) x(1,4) ; x(1,4) x(4,4)];
Y(3:4,3:4) = [x(3,3) x(6,3) ; x(6,3) x(6,6)];