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Re: an issue of consistency

  • To: mathgroup at smc.vnet.net
  • Subject: [mg112380] Re: an issue of consistency
  • From: "Kevin J. McCann" <Kevin.McCann at umbc.edu>
  • Date: Sat, 11 Sep 2010 05:46:12 -0400 (EDT)
  • References: <i6csi4$t2m$1@smc.vnet.net>

I would say that such behavior is *clearly* inconsistent, especially 
since the use of the two examples below would require that you actually 
know that one answer is algebraic and the other not in order to modify 
the code appropriately. Of course in this example it is obvious, but I 
can imagine a large looped calculation which produces both types and you 
don't have the luxury of checking each one.

Kevin

On 9/10/2010 5:08 AM, Andrzej Kozlowski wrote:
> This post is about a mild dispute I have been having with Wolfram's
> technical support. It concerns behaviour that I see as inconsistent and
> Technical Support seems to insist otherwise. I would not claim that it
> actually represents a "bug" but I discovered it in a "real life"
> situation, it was unexpected and took a while to see what the cause of
> it was.
> In any case, I am not writing to "complain", but to find out if anyone
> can justify the behaviour that I am going to describe as "consistent".
> Technical Support thinks it is, but I can't understand their reasoning.
>
> Consider the two "root object" numbers:
>
> a = Root[#1^5 - # + 1&, 1];
> b = Root[#1^5 - # + Log[2]&, 1];
>
> The first is an algebraic number, the second is not, but they are both
> real numbers which can be computed to arbitrary precision, e.g.
>
>   N[{a, b}, 10]
>
> {-1.167303978,-1.127288474}
>
> O.K. now compare this:
>
> Graphics[Point[{{Root[#1^5 - # + 1&, 1], 0}}]]
>
> and this:
>
> Graphics[Point[{{Root[#1^5 - # + Log[2]&, 1], 0}}]]
>
> In the first case Graphics forces N to be automatically applied while in
> the second case one needs to do so manually:
>
> Graphics[Point[{{Root[#1^5 - # + Log[2]&, 1], 0}}]]//N
>
> This seems to me to be inconsistent, or at least I do not know of nay
> obvious reason why the first number being algebraic and the second
> number not being so should make any difference to how they are treated
> by Graphics. Technical Support claims otherwise but is unable to provide
> a reason that I can understand. Can anyone else?
>
> Andrzej Kozlowski
>
>
>


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