Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2006
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: SetPrecision vs N

  • To: mathgroup at smc.vnet.net
  • Subject: [mg71714] Re: SetPrecision vs N
  • From: Peter Pein <petsie at dordos.net>
  • Date: Mon, 27 Nov 2006 04:04:37 -0500 (EST)
  • Organization: 1&1 Internet AG
  • References: <ekbmmt$f9g$1@smc.vnet.net>

Andrew Moylan schrieb:
> Hi all,
> 
> Suppose I want to evaluate an expression at a given precision. What is
> the difference between using N[expr, precision] and using
> SetPrecision[expr, precision]?
> 
> I've noticed that SetPrecision seems to be equivalent even in such
> situations as e.g. N[Integrate[...]] automatically calling
> NIntegrate[...] when the integral can't be done exactly:
> 
> SetPrecision[Integrate[x^x, {x, 0, 1}], 20]
>   and
> N[Integrate[x^x, {x, 0, 1}], 20]
>   both give
> 0.78343051071213440706
> 
> Are there important differences between SetPrecision and N that I
> should be aware of?
> 
> Cheers,
> Andrew
> 

Hi Andrew,

the most obvious difference is:

Precision[N[1.1, 1000]]
--> MachinePrecision

vs.

Precision[SetPrecision[1.1, 1000]]
-->1000.

I guess, SetPrecision[#,prec]& automagically applies N[#,prec]& to an
expression having greater precision than prec (especially when applied to
exact expressions (which got infinite precision)).

P²


  • Prev by Date: Please help carry out the integral
  • Next by Date: Re: Re: Re: 1`2 == 1*^-10
  • Previous by thread: Re: SetPrecision vs N
  • Next by thread: Re: SetPrecision vs N