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MathGroup Archive 2005

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Re: Globally limiting precision or accuracy

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61024] Re: [mg61010] Globally limiting precision or accuracy
  • From: jmt <jmt at dxdydz.net>
  • Date: Sat, 8 Oct 2005 02:48:30 -0400 (EDT)
  • Organization: dxdydz
  • References: <200510070737.DAA03251@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

- I don't think reducing $MachinePrecision below the default value for your 
workstation will improve speed, since calculation are probably done using the 
floating-point capabilities of your cpu ;

- Check if you ever do use extended precision numbers ;

- Try to use integer arithmetic instead of floating point arithmetic ;

- Check for useless calculations, e.g. computation involving euclidian 
distance can generally be performed on Power[distance,2], taking a square 
root is useless.

jmt 

On Friday 07 October 2005 09:37, Lee Newman wrote:
> 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


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