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MathGroup Archive 2000

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RE: How to display the desired numerical precision?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg25246] RE: [mg25215] How to display the desired numerical precision?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sun, 17 Sep 2000 04:47:24 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Christopher,

WRI has changed the behavior of N over versions. It never was meant for
formatting numbers. It's basic purpose is to convert exact numbers to
approximate numbers. If the precision specified is less than or equal to
machine precision it uses machine precision. If it is greater, it uses
extended precision approximate numbers.

Use NumberForm to control the display of your numbers.

The display of machine precision numbers can be set with the Option
Inspector.
FormattingOptions/ExpressionFormatting/DisplayOptions/PrintPrecision.

Another option is to use SetPrecision which allows precisions of less than
machine precision also. See Sections 3.1.4 to 3.1.6 in the Mathematica Book.

But what you probably really want is NumberForm.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/


> -----Original Message-----
> From: Christopher R. Carlen [mailto:crcarle at sandia.gov]
To: mathgroup at smc.vnet.net

> Hi:
>
> In Mathematica 3, I could input
>
> N[ Pi, 12 ]
>
> and see 12 digits of result.  However in Mathematica 4 I see 6
> digits, no matter
> what I put in for the number of digits, unless >16.  In other words,
>
> N[ Pi, 17 ]
>
> shows 17 digits.
>
> It seems that for less than or equal to machine precision, the result
> gets displayed using the setting of Formatting Options|Expression
> Formatting|Display OPtions|Print Precision.
>
> But for numbers greater than the maching precision, the result displays
> according the precision specified to the N function.
>
> Can someone tell me how to get the following behavior from Mathematica 4:
>
> If I don't specify anything about precision, show 6 digits.
>
> Else if I specify any number of digits to N[] from 1 to n, then display
> n digits.
>
> Thanks for input.
> --
> _______________________
> Christopher R. Carlen
> Sr. Laser/Optical Tech.
> Sandia National Labs
>
>



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