How to generate a sparse matrix for a given array?
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Dear All,
I want to generate a sparse matrix B for a given array A. A contains two columns of indecis. For example,
A = [1 3;
1 4;
2 3;
2 5;
3 5;
4 5]
The sparse matrix B should be as follows:
B = [ 2 0 -1 -1 0;
0 2 -1 0 -1;
-1 -1 2 0 0;
-1 0 0 2 -1;
0 -1 -1 -1 3]
The characteristics of B:
- Sum of each row is zero.
- If we consider matrix A gives the information of edges of a graph, B(i,i) = sum of number of edges, B(i,j) = -1 if there is an edge between i and j.
Thanks a lot.
Benson
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the cyclist
2021-5-24
Here is one way:
A = [1 3;
1 4;
2 3;
2 5;
3 5;
4 5];
d = max(A(:));
B = sparse(A(:,1),A(:,2),-1,d,d) + sparse(A(:,2),A(:,1),-1,d,d);
for ii = 1:d
B(ii,ii) = -sum(B(ii,:));
end
disp(B)
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the cyclist
2021-5-25
A=unique(sort(A,2),'rows')
is what you would need to do here as well.
If you posted a small example that exhibits the problem, it would help. But I'm guessing you have your answer.
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