diff --git a/ncm.py b/ncm.py
index 0bff27c..56c4d03 100644
--- a/ncm.py
+++ b/ncm.py
@@ -56,7 +56,9 @@ def pearson_def(x, y):
         xdiff2 += xdiff * xdiff
         ydiff2 += ydiff * ydiff
 
-    return diffprod / math.sqrt(xdiff2 * ydiff2)
+    sqrt_xdiff2_ydiff2 = math.sqrt(xdiff2 * ydiff2)
+
+    return diffprod / sqrt_xdiff2_ydiff2 if sqrt_xdiff2_ydiff2 != 0.0 else 0.0
 
 # createDataSet
 # base_dir : directory of files, bedFile: name of the bedFile
@@ -251,7 +253,7 @@ def createDataSetFromList(base_list, bedFile):
         link = line.strip()
         f = open(link, "r")
         dbsnpf= open(bedFile,"r")
-        file = link[link.rindex("/")+1:]
+        file = os.path.basename(link)
         depth = dict()
         depth[file] = 0
         real_count[file] = 0