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Simple triangle enumeration julia
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using SparseArrays | |
function find_triangles(A::SparseMatrixCSC{Int64,Int64}) | |
n = size(A, 1) # number of nodes | |
d = vec(sum(A, dims=2)) # degree vector | |
deg_order = zeros(Int64, n) | |
deg_order[sortperm(d)] = 1:n | |
triangles = [] | |
for i = 1:n | |
N_i = findnz(A[:, i])[1] # neighbors of node i | |
# only look over pairs of neighbors with higher degree order | |
N_i_keep = [j for j in N_i if deg_order[j] > deg_order[i]] | |
for jj = 1:length(N_i_keep) | |
for kk = (jj + 1):length(N_i_keep) | |
j = N_i_keep[jj] | |
k = N_i_keep[kk] | |
# check for triangle | |
if A[j, k] > 0 | |
# triangle (i, j, k) | |
push!(triangles, (i, j, k)) | |
end | |
end | |
end | |
end | |
return triangles | |
end |
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