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MathGroup Archive 2002

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Re: Significance Arithmetic

  • To: mathgroup at smc.vnet.net
  • Subject: [mg37014] Re: Significance Arithmetic
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Sun, 6 Oct 2002 05:33:12 -0400 (EDT)
  • References: <000001c26bd9$e486f400$0300a8c0@HolyCow>
  • Sender: owner-wri-mathgroup at wolfram.com

Bobby,

One point:

>.... bigfloats ...  [are] the result of using N[expr,k] or 
SetAccuracy[expr,k] where k is bigger than machine precision.  If k <=
> machine > precision, the result is a machine precision number.

We get bigfloats with k<=machine precision with SetAccuracy and 
SetPrecision but not with N:

Example

    a=SetPrecision[2.3,5]
        2.3000

    Precision[a]

        5.

    Precision[a^2000]

        1.69897

Also, of course, when more than machine precision significant digits are 
given

    a=1.01234567891234500;

    Precision[a]

        17.301


Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565



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