Creating a submatrix from a matrix

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Konstantinos
Konstantinos 2014-12-4
评论： Gabriele Bunkheila 2024-12-3
I want a code to create a matrix which consist of rows and columns of another matrix.
i.e. A (4X4) = [ 1 2 3 4; 5 6 7 8; 1 3 5 7; 2 4 6 8; ]
The submatrix B consist of the { 1, 2, 4 }rows of A and the { 2,3 }columns of A:
Β (3Χ2) = [ 2 3; 6 7; 4 6; ]
Any help could be useful.
Thanks in advance!
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said mohamed
said mohamed 2021-5-5
Using the matrix A = [5 1 11; 7 13 3; 8 5 2], the matrix B is constructed as B = [A A A; A A A; A A A]. Which of the following is the result of the operation K = L * J, made using the submatrices of matrix B, L = B (1: 3,3: 5) and J = B (2: 4,2: 3)?

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Azzi Abdelmalek
Azzi Abdelmalek 2014-12-4
编辑：Azzi Abdelmalek 2014-12-4
A= [ 1 2 3 4; 5 6 7 8; 1 3 5 7; 2 4 6 8; ]
B=A([1 2 4],[2 3])
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said mohamed
said mohamed 2021-5-5
Using the matrix A = [5 1 11; 7 13 3; 8 5 2], the matrix B is constructed as B = [A A A; A A A; A A A]. Which of the following is the result of the operation K = L * J, made using the submatrices of matrix B, L = B (1: 3,3: 5) and J = B (2: 4,2: 3)?

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VANSHUL CHOUDHARY
VANSHUL CHOUDHARY 2021-8-20
A = rand(4,3);
% Get those elements of A that are located in rows 3 to 4 and
% column 2 to 3.
sub_matrix = A(3:4,2:3);
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Gabriele Bunkheila
Gabriele Bunkheila 2024-12-3
Ran in:
Please note:
  1. With matrices, the first dimesion is always the number of row, the second is the number of columns. So in this case A is 5x5 (size(A) would return [5,5]) and A4 is 4x2 (size(A4) would return [4,2]).
  2. A4 here seems composed of two "stacked" (or vertically concatenated) 2x2 sub-matrices of A
A possible way to obtain A4 from A is the following;
A = [1:5; 0.5*(-10:-6); 0.1*0:4; 10:-1:6; 2*(1:5)]
A = 5×5
1.0000 2.0000 3.0000 4.0000 5.0000 -5.0000 -4.5000 -4.0000 -3.5000 -3.0000 0 1.0000 2.0000 3.0000 4.0000 10.0000 9.0000 8.0000 7.0000 6.0000 2.0000 4.0000 6.0000 8.0000 10.0000
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rows1 = [1, 2];
cols1 = [1, 2];
rows2 = [3, 4];
cols2 = [3, 4];
A4 = [A(rows1, cols1); A(rows2, cols2)]
A4 = 4×2
1.0000 2.0000 -5.0000 -4.5000 2.0000 3.0000 8.0000 7.0000
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@Ioannis Aggelos I hope this helps.

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