running kmeans with --vec takes longer than without

[philipportner]

When running the following kmeans script, adding the --vec flag increases the runtime of the program by a bit more than 50%.

kmeans.daphne

Same script can be found in test/api/cli/algorithms/kmeans.daphne

// K-means clustering.

// Arguments:
// - r ... number of records
// - c ... number of centroids
// - f ... number of features
// - i ... number of iterations

// Data generation.
X = rand($r, $f, 0.0, 1.0, 1, -1);
C = rand($c, $f, 0.0, 1.0, 1, -1);

// K-means clustering (decisive part).
for(i in 1:$i) {
    D = (X @ t(C)) * -2 + t(sum(C ^ 2, 0));
    minD = aggMin(D, 0);
    P = D <= minD;
    P = P / sum(P, 0);
    P_denom = sum(P, 1);
    C = (t(P) @ X) / t(P_denom);
}

// Result output.
print(C);

cli command to run kmeans.daphne

time bin/daphne test/api/cli/algorithms/kmeans.daphne r=1000000 f=100 c=50 i=10

time bin/daphne --vec test/api/cli/algorithms/kmeans.daphne r=1000000 f=100 c=50 i=10

time output

bin/daphne test/api/cli/algorithms/kmeans.daphne r=1000000 f=100 c=50 i=10 115.16s user 136.03s system 1109% cpu 22.634 total

bin/daphne --vec test/api/cli/algorithms/kmeans.daphne r=1000000 f=100 c=50 461.03s user 821.06s system 3718% cpu 34.477 total