From 9caccda16491253668c7a928cf7e7d631c3a6424 Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <inform@tiker.net>
Date: Sun, 5 Jun 2016 19:48:28 -0500
Subject: [PATCH] Spatial binary tree: prevent infinite recursion by
probabilistic retention
---
pytools/spatial_btree.py | 36 ++++++++++++++++++++++++------------
1 file changed, 24 insertions(+), 12 deletions(-)
diff --git a/pytools/spatial_btree.py b/pytools/spatial_btree.py
index 00adc20..dba6ec8 100644
--- a/pytools/spatial_btree.py
+++ b/pytools/spatial_btree.py
@@ -85,9 +85,22 @@ class SpatialBinaryTreeBucket:
"""
def insert_into_subdivision(element, bbox):
- for bucket in self.all_buckets:
- if do_boxes_intersect((bucket.bottom_left, bucket.top_right), bbox):
- bucket.insert(element, bbox)
+ bucket_matches = [
+ ibucket
+ for ibucket, bucket in enumerate(self.all_buckets)
+ if do_boxes_intersect((bucket.bottom_left, bucket.top_right), bbox)]
+
+ from random import uniform
+ if len(bucket_matches) > len(self.all_buckets) // 2:
+ # Would go into more than half of all buckets--keep it here
+ self.elements.append((element, bbox))
+ elif len(bucket_matches) > 1 and uniform(0, 1) > 0.95:
+ # Would go into more than one bucket and therefore may recurse
+ # indefinitely. Keep it here with a low probability.
+ self.elements.append((element, bbox))
+ else:
+ for ibucket_match in bucket_matches:
+ self.all_buckets[ibucket_match].insert(element, bbox)
if self.buckets is None:
# No subdivisions yet.
@@ -99,14 +112,13 @@ class SpatialBinaryTreeBucket:
self.all_buckets,
max_elements_per_box=self.max_elements_per_box)
+ old_elements = self.elements
+ self.elements = []
+
# Move all elements from the full bucket into the new finer ones
- for el, el_bbox in self.elements:
+ for el, el_bbox in old_elements:
insert_into_subdivision(el, el_bbox)
- # Free up some memory. Elements are now stored in the
- # subdivision, so we don't need them here any more.
- del self.elements
-
insert_into_subdivision(element, bbox)
else:
# Simple:
@@ -128,10 +140,10 @@ class SpatialBinaryTreeBucket:
for result in bucket.generate_matches(point):
yield result
- else:
- # We don't. Perform linear search.
- for el, bbox in self.elements:
- yield el
+
+ # Perform linear search.
+ for el, bbox in self.elements:
+ yield el
def visualize(self, file):
file.write("%f %f\n" % (self.bottom_left[0], self.bottom_left[1]))
--
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