# how to get B+ matrix (warshall algorithm) in matlab?

Pseudocode:

// B = nxn binary matrix
// Bm = resulting matrix
for (i=1; i<=n; i++)
{
for (j=1; j<=n; j++)
{
if (B[i,j] == 1)
{
for (k=1; k<=n; k++)
{
Bm[i,j] = B[i,j] | B[k,j];
}
}
}
}


This is the warshall algorithm written (in my way) in matlab:

B = [1 1 0 0 0; 0 0 0 1 0; 0 0 0 0 1; 0 1 0 0 0; 0 0 0 0 0];

n = 5;

Bm = zeros(n);

for i = 1:n
for j = 1:n
if B(i,j) == 1
for k = 1:n
Bm(i,k) = B(i,k) | B(k,j);
end
end
end
end


It works but, how can I improve the matrix loops?

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Did you mean Bm(i,j) = B(i,k) | B(k,j)? –  Quentin Pradet May 7 '13 at 13:48

Furthermore, one way to speed up your code is to use a short circuit logical operator:

B(i,k) || B(k,j);


Also it seems to have a small effect if you use a logical matrix as input rather than a double:

B = logical(b);


Last and least, it would be nicer to initialize Bm with the datatype that it will have:

Bm = false(n)

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