From e36d1c2e0ebbe0664d6402a07191b7957718f94d Mon Sep 17 00:00:00 2001
From: jgoecks <jgoecks@gwu.edu>
Date: Fri, 24 Jul 2015 16:45:18 -0400
Subject: [PATCH] Fix BBI data provider underflow bug when computing standard
 deviation

---
 lib/galaxy/visualization/data_providers/genome.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/galaxy/visualization/data_providers/genome.py b/lib/galaxy/visualization/data_providers/genome.py
index bebbede5fc8..8504c87889d 100644
--- a/lib/galaxy/visualization/data_providers/genome.py
+++ b/lib/galaxy/visualization/data_providers/genome.py
@@ -1180,7 +1180,7 @@ class BBIDataProvider( GenomeDataProvider ):
                     # Compute $\mu \pm 2\sigma$ to provide an estimate for upper and lower
                     # bounds that contain ~95% of the data.
                     mean = summary.sum_data[0] / valid_count
-                    var = summary.sum_squares[0] - mean
+                    var = max( summary.sum_squares[0] - mean, 0 ) # Prevent variance underflow.
                     if valid_count > 1:
                         var /= valid_count - 1
                     sd = math.sqrt( var )