Removed the cosine similarity since it's not a true distance metric. Use the arccos distance instead

Author: Bruno Alano

hdbscan/dist_metrics.pyx

@@ -1040,20 +1040,20 @@ cdef class HaversineDistance(DistanceMetric):
 #------------------------------------------------------------
 # Cosine Distance
 #  D(x, y) = dot(x, y) / (|x| * |y|)
-# [This is not a true metric, so we will leave it out.]
+# [This is not a true metric, so we will leave it out. Use the `arccos` distance instead]
 
-cdef class CosineDistance(DistanceMetric):
-    cdef inline DTYPE_t dist(self, DTYPE_t* x1, DTYPE_t* x2, ITYPE_t size) nogil except -1:
-        cdef DTYPE_t d = 0, norm1 = 0, norm2 = 0
-        cdef np.intp_t j
-        for j in range(size):
-            d += x1[j] * x2[j]
-            norm1 += x1[j] * x1[j]
-            norm2 += x2[j] * x2[j]
-        return 1.0 - d / sqrt(norm1 * norm2)
+#cdef class CosineDistance(DistanceMetric):
+#    cdef inline DTYPE_t dist(self, DTYPE_t* x1, DTYPE_t* x2, ITYPE_t size) nogil except -1:
+#        cdef DTYPE_t d = 0, norm1 = 0, norm2 = 0
+#        cdef np.intp_t j
+#        for j in range(size):
+#            d += x1[j] * x2[j]
+#            norm1 += x1[j] * x1[j]
+#            norm2 += x2[j] * x2[j]
+#        return 1.0 - d / sqrt(norm1 * norm2)
 
 #------------------------------------------------------------
-# Cosine Distance
+# Arccos Distance
 #  D(x, y) = arccos(dot(x, y) / (|x| * |y|)) / PI
 
 cdef class ArccosDistance(DistanceMetric):