math lib change in OS X bug + workaround
- To: mathgroup at smc.vnet.net
- Subject: [mg108833] math lib change in OS X bug + workaround
- From: Paul Makepeace <paulm at paulm.com>
- Date: Fri, 2 Apr 2010 05:21:25 -0500 (EST)
(Not sure if this has already been posted; sorry if this is old news.)
I recently noticed FixedPointList[Cos, .7] does not complete with
7.0.1 on OS X 10.6.3 -- symptoms are Mathematica is stuck
"Running...".
After some digging it turns out it's oscillating indefinitely. Here's
my edited exchange with WRI support:
---
If I put a limit on the invocation it returns, then "Raw Form" shows
the numbers are oscillating, presumably related to some precision
issue.
FixedPointList[Cos, .7, 500]
0.7390851332151605, 0.7390851332151608, 0.7390851332151605,
0.7390851332151608, 0.7390851332151605
---
WRI support replied,
Hello,
Thank you for the email.
First I think is kernel problem. But it turned out it is not. I can
reproduce this problem on my Mac machine. And I have consulted this
problem with our development group. This is caused by the recent change of
math library of OSX. The workaround might be specifying SameTest function,
see below:
In[1]:= FixedPointList[Cos, .7, SameTest -> (Equal[N[#1], N[#2]] &)]
Out[1]= {0.7, 0.764842, 0.721492, 0.750821, 0.731129, 0.744421, \
0.73548, 0.741509, 0.73745, 0.740185, 0.738344, 0.739584, 0.738749, \
0.739312, 0.738932, 0.739188, 0.739016, 0.739132, 0.739054, 0.739106, \
0.739071, 0.739095, 0.739079, 0.739089, 0.739082, 0.739087, 0.739084, \
0.739086, 0.739085, 0.739086, 0.739085, 0.739085, 0.739085, 0.739085, \
0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, \
0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, \
0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, \
0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, \
0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, \
0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, 0.739085, \
0.739085}
I have forwarded your examples to our development group and have included
your contact information so that you can be notified when this has been
resolved.
---
HTH, Paul