[Python-checkins] r69761 - python/trunk/Doc/library/math.rst

Thu Feb 19 06:51:41 CET 2009

Author: raymond.hettinger
Date: Thu Feb 19 06:51:41 2009
New Revision: 69761
Log:
Add an example for math.fsum() and elaborate on the accurary note.
Modified:
 python/trunk/Doc/library/math.rst
Modified: python/trunk/Doc/library/math.rst
==============================================================================

--- python/trunk/Doc/library/math.rst	(original)
+++ python/trunk/Doc/library/math.rst	Thu Feb 19 06:51:41 2009
@@ -87,14 +87,18 @@
 .. function:: fsum(iterable)
 
 Return an accurate floating point sum of values in the iterable. Avoids
- loss of precision by tracking multiple intermediate partial sums. The
- algorithm's accuracy depends on IEEE-754 arithmetic guarantees and the
- typical case where the rounding mode is half-even.
+ loss of precision by tracking multiple intermediate partial sums::
 
- .. note::
-
- The accuracy of fsum() may be impaired on builds that use
- extended precision addition and then double-round the results.
+ >>> sum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1])
+ 0.99999999999999989
+ >>> fsum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1])
+ 1.0
+
+ The algorithm's accuracy depends on IEEE-754 arithmetic guarantees and the
+ typical case where the rounding mode is half-even. On some non-Windows
+ builds, the underlying C library uses extended precision addition and may
+ occasionally double-round an intermediate sum causing it to be off in its
+ least significant bit.
 
 .. versionadded:: 2.6
 
