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Globally limiting precision or accuracy

• To: mathgroup at smc.vnet.net
• Subject: [mg61010] Globally limiting precision or accuracy
• From: Lee Newman <leenewm at umich.edu>
• Date: Fri, 7 Oct 2005 03:37:57 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

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

• Follow-Ups:
  • Re: Globally limiting precision or accuracy
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>
  • Re: Globally limiting precision or accuracy
    • From: jmt <jmt@dxdydz.net>
  • Re: Globally limiting precision or accuracy
    • From: Sseziwa Mukasa <mukasa@jeol.com>