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Re: "Sloppy Union"? (Union of a list with *nearly* equ

  • To: mathgroup at smc.vnet.net
  • Subject: [mg42061] Re: "Sloppy Union"? (Union of a list with *nearly* equ
  • From: Bill Rowe <listuser at earthlink.net>
  • Date: Tue, 17 Jun 2003 05:44:09 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 6/16/03 at 3:56 AM, akgandhi at uchicago.edu (Amit Gandhi) wrote:

>I often try to use the N[] function to chop or round a number to so
>many digits - but if I choose the number of digits desired to be small
>such as N[x, 3] or N[x,4] it does not appear to have any effect and
>the result remains in 6 digit format...,

Right. Anytime you ask for fewer digits than machine precision N defaults to a machine precision number. I assume that is because there is little or no advantage to lower than machine precision.

>more generally - suppose you are performing a series of calculations
>and you wish for the the output value x of each calculation to be
>chopped before being input to the next calculation, does it suffice to
>enter the input as N[x, 3]??

No, this won't suffice. N isn't intended to control the output display. More to the point why would you want to reduce the precision of intermediate computations? You can always reduce the precision of the final answer to anything desired. And if you chop intermediate results to a specified precision, the final answer will have still lower precision since any lack of precision builds with each computation.


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