# [Matrix-SIG] precision of numbers

**Paul F. Dubois
**
Paul F. Dubois" <dubois1@llnl.gov

*Fri, 3 Apr 1998 07:52:54 -0800*

For many functions an actual zero does not exist on a computer. One correct
way to do bisection is to pick an epsilon e and stop when
(upper-lower)/(upper+lower) < e/2. At that point f(upper)*f(lower) <= 0.0
and you can choose upper, lower, or (upper+lower)/2.0 as your "root".
-----Original Message-----
From: Dave Stinchcombe <dars@soton.ac.uk>
To: matrix-sig@python.org <matrix-sig@python.org>
Date: Friday, April 03, 1998 2:19 AM
Subject: [Matrix-SIG] precision of numbers
>*Hello again,
*>*
*>*I've been doing some more work (shock horror), and this time I want to be
*>*able to increase the precision of calculation. This is because I can't seem
*>*to make a parameter move in small enough steps to pick up a solution where
*>*I know one exists. At the moment I recursively increase precision in
*>*traditional bisection fashion, until a zero is found, except I run out of
*>*precision. Zero is obviously a very small number and not an actual zero,
*>*I chose |1e-10|.
*>*
*>*Is there another number type, or is there a precision parameter in Numpy,
*>*or can I fool it with a simple trick(I can think of one for my particular
*>*problem, but howabout in general)??? All answers gratefully received.
*>*
*>*Yours
*>*Dave
*>*
*>*
*>*
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