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Re: Globally limiting precision or accuracy

• To: mathgroup at smc.vnet.net
• Subject: [mg61038] Re: Globally limiting precision or accuracy
• From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
• Date: Sat, 8 Oct 2005 02:48:53 -0400 (EDT)
• Organization: Uni Leipzig
• References: <di59ru$3it$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

Mathematica wil always use at least the machine precision and
it would not increase the speed when you use fewer digits, because
the arithmetic is done by the floating point hardware of your computer
and it would take more time to pass the two terms to the FPU, do the operation
and round the result to 3 digits, than to pass the terms and do the operation.

Regards
  Jens

"Lee Newman" <leenewm at umich.edu> schrieb im 
Newsbeitrag news:di59ru$3it$1 at smc.vnet.net...
| Dear Group,
|
| Situation
| -  I have a large neural network model (my own 
code, not Wolfram's
| toolbox) that currently has a run time of about 
20hours.
| -  I am in the process of trying to profile and 
optimize the code
| (mostly matrix computations) to reduce the run 
time.
| -  All of the computationas that I do are 
numerical.
|
| Questions
| (1) If I am not concerned about numerical 
accuracy beyond 3 decimal
| places for any of the computations in the model, 
can I improve
| performance by telling mathematica to globally 
restrict its accuracy (or
| precision) for all computations?
|
| (2) If so, how do I do this?  Is it as simple as 
setting
| $MachinePrecision=3?  Is there a global way 
(rather than local use of
| N[]) to ensure that all computations are done 
numerically, and with
| machine precision?
|
| Thanks,
| Lee Newman
|