Matrix symmetric by 2x2 blocks
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Hello everyone,
I need to extract from 2n by 2n matrix the symetric and skew-symetric 2x2 blocks.
For example, for given A:
A=[
5,-1, 2,-3;
1,5, 4,2;
-2,3, 5,-1;
4,-2, 1,5;
]
I want to get:
A_symetric= [
5,-1, 0,0;
1,5, 4,0;
0,0, 5,-1;
4,0, 1,5;
]
And
A_skew_symetric= [
0,0, 2,3;
0,0, 0,2;
-2,-3, 0,0;
0,-2, 0,0;
]
2 Comments
Ohad Shapira
on 9 Jan 2021
function [A_sym,A_anti] = sym_by_blocks(A)
syms w t
n=length(A);
A_sym=sym(zeros(length(A)));
A_anti=sym(zeros(length(A)));
for row=1:2:n
for col=1:2:n
if row==col
A_sym(row:row+1,col:col+1)=A(row:row+1,col:col+1);
else
A_sym(row:row+1,col:col+1)=0.5*(A(row:row+1,col:col+1)+A(col:col+1,row:row+1));
A_anti(row:row+1,col:col+1)=0.5*(A(row:row+1,col:col+1)-A(col:col+1,row:row+1));
end
end
end
end
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