create a matrix from matrix with zeros elements

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Ali Tawfik
Ali Tawfik 2020-1-24
回答： Sindar 2020-1-29
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,
  2 个评论
Sindar
Sindar 2020-1-24
what is the logic of which elements are zero, and what value the non-zero ones take?
Ali Tawfik
Ali Tawfik 2020-1-27
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,

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回答（2 个）

Spencer Chen
Spencer Chen 2020-1-24
You can create a new matrix of the same size:
B = zeros(size(A));
Then assign non-zero data in B.
Blessings,
Spencer
  1 个评论
Ali Tawfik
Ali Tawfik 2020-1-27
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,

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Sindar
Sindar 2020-1-29
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)];

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