How to create a symmetrical matrix?
150 visualizaciones (últimos 30 días)
Mostrar comentarios más antiguos
ric1321
el 3 de Feb. de 2017
Hi, I have to fill a matrix with some data that come from a subroutine. The matrix is symmetrical over the two diagonals, so I have to build just a quarter of it and then to copy one the other parts. How can I do?
1 comentario
Respuesta aceptada
Stephen23
el 3 de Feb. de 2017
Editada: Stephen23
el 3 de Feb. de 2017
I looked at this task, and tried several possibilities to convert this:
>> M = [1,2,3,4,5;0,6,7,8,0;0,0,9,0,0;0,0,0,0,0;0,0,0,0,0]
M =
1 2 3 4 5
0 6 7 8 0
0 0 9 0 0
0 0 0 0 0
0 0 0 0 0
But then it occurred to me: the question states "I have to fill a matrix with some data that come from a subroutine", so perhaps the simplest way is to avoid it all together: if you have to fill the matrix with these values (presumably in a loop and using some indexing), then instead of just filling one value, fill in all four values at once. This is likely going to be simpler than any method of taking that quarter matrix, rotating, and merging again...
So the simplest way for your situation might be to not "copy and rotate", but to allocate each new value to four locations when you put it into the matrix:
S = size(M);
[R,C] = find(M);
Z = nan(S);
for k = 1:numel(R) % for each subroutine value
x = [R(k),1+S(1)-R(k),C(k),1+S(2)-C(k)]; % index
m = M(R(k),C(k)); % new subroutine value here
Z(x,x) = m;
end
which gives this:
Z =
5 4 3 4 5
4 8 7 8 4
3 7 9 7 3
4 8 7 8 4
5 4 3 4 5
Or you can use the method exactly as I did here: to copy the elements of that quarter to the other quarters.
0 comentarios
Más respuestas (2)
Benjamin Klassen
el 26 de En. de 2023
Symmetric Matrix Generator
% Rows
r1=[1,2,3,4,5,6,7,8];
r2=[5,2,6,7,9,8,5];
r3=[1,4,6,2,8,6];
r4=[1,6,2,9,4];
r5=[1,3,2,7];
r6=[1,7,9];
r7=[6,2];
r8=[9];
nr=length(r1); % Number of rows
K=zeros(nr,nr);
% Symmetric Matrix Assembly
for i=1:nr
d=join(['r',num2str(i)])
rowvalues=eval(d);
K(i,i:end)=rowvalues;
K(i:end,i)=rowvalues;
end
Ver también
Categorías
Más información sobre Operating on Diagonal Matrices en Help Center y File Exchange.
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!