// Executes a k-means step with a KmTree on the given point-set with the given set of centers, and
// tests if it is correct by comparing results with the naive O(nkd) implementation. The cost is
// returned, which is used to determine when k-means has finished.
//
// Generates an assertion failure if there is an error.
Scalar TestKMeansStep(const KmTree &tree, int n, int k, int d, Scalar *points, Scalar *centers) {
// Allocate memory
int *assignment = (int*)malloc(n * sizeof(int));
Scalar *old_centers = (Scalar*)malloc(k * d * sizeof(Scalar));
Scalar *new_sums = (Scalar*)calloc(k * d, sizeof(Scalar));
int *new_counts = (int*)calloc(k, sizeof(int));
Scalar *bad_center = PointAllocate(d);
if (assignment == 0 || old_centers == 0 || new_sums == 0 || new_counts == 0 || bad_center == 0)
MemoryAssertFail("running unit test");
memset(bad_center, 0xff, d * sizeof(Scalar));
memcpy(old_centers, centers, k * d * sizeof(Scalar));
// Run fancy k-means
Scalar fancy_cost = tree.DoKMeansStep(k, centers, assignment);
// Test the assignments and build the correct aggregate data
Scalar correct_cost = 0;
for (int i = 0; i < n; i++) {
Scalar fancy_dist_sq = PointDistSq(points + i*d, old_centers + assignment[i]*d, d);
for (int j = 0; j < k; j++)
if (memcmp(old_centers + j*d, bad_center, d*sizeof(Scalar)) != 0) {
Scalar dist_sq = PointDistSq(points + i*d, old_centers + j*d, d);
UnitTestAssert(TestScalarsGe(dist_sq, fancy_dist_sq),
"k-means assigned point to the wrong cluster");
}
// Note that the cost is measured from the OLD centers, not from the new centers
correct_cost += fancy_dist_sq;
PointAdd(new_sums + assignment[i]*d, points + i*d, d);
new_counts[assignment[i]]++;
}
// Test the costs
UnitTestAssert(TestScalarsEq(correct_cost, fancy_cost),
"k-means calculated the cost function incorrectly");
// Test the centers
for (int i = 0; i < k; i++) {
bool fancy_is_void = (memcmp(centers + i*d, bad_center, d*sizeof(Scalar)) == 0);
bool correct_is_void = (new_counts[i] == 0);
UnitTestAssert(fancy_is_void == correct_is_void,
"k-means failed to correctly mark whether a center was being used");
if (!fancy_is_void) {
PointScale(new_sums + i*d, Scalar(1) / new_counts[i], d);
for (int j = 0; j < d; j++) {
UnitTestAssert(TestScalarsEq(new_sums[i*d + j], centers[i*d + j]),
"k-means failed to set a center correctly");
}
}
}
// Free memory
PointFree(bad_center);
free(new_counts);
free(new_sums);
free(old_centers);
free(assignment);
return fancy_cost;
}
// See KMeans.h
// Performs one full execution of k-means, logging any relevant information, and
// tracking meta
// statistics for the run. If min or max values are negative, they are treated
// as unset.
// best_centers and best_assignment can be 0, in which case they are not set.
static void RunKMeansOnce(
const KmTree& tree, int n, int k, int d, Scalar* points, Scalar* centers,
Scalar* min_cost, Scalar* max_cost, Scalar* total_cost, double start_time,
double* min_time, double* max_time, double* total_time,
Scalar* best_centers, int* best_assignment)
{
MRPT_UNUSED_PARAM(n);
MRPT_UNUSED_PARAM(points);
const Scalar kEpsilon =
Scalar(1e-8); // Used to determine when to terminate k-means
// Do iterations of k-means until the cost stabilizes
Scalar old_cost = 0;
bool is_done = false;
for (int iteration = 0; !is_done; iteration++)
{
Scalar new_cost = tree.DoKMeansStep(k, centers, 0);
is_done = (iteration > 0 && new_cost >= (1 - kEpsilon) * old_cost);
old_cost = new_cost;
LOG(true, "Completed iteration #" << (iteration + 1) << ", cost="
<< new_cost << "..." << endl);
}
double this_time = GetSeconds() - start_time;
// Log the clustering we found
LOG(false, "Completed run: cost=" << old_cost << " (" << this_time
<< " seconds)" << endl);
// Handle a new min cost, updating best_centers and best_assignment as
// appropriate
if (*min_cost < 0 || old_cost < *min_cost)
{
*min_cost = old_cost;
if (best_assignment != 0)
tree.DoKMeansStep(k, centers, best_assignment);
if (best_centers != 0)
memcpy(best_centers, centers, sizeof(Scalar) * k * d);
}
// Update all other aggregate stats
if (*max_cost < old_cost) *max_cost = old_cost;
*total_cost += old_cost;
if (*min_time < 0 || *min_time > this_time) *min_time = this_time;
if (*max_time < this_time) *max_time = this_time;
*total_time += this_time;
}
