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MathGroup Archive 2001

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Re: How do I eliminate premultipliers of "1." ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31162] Re: How do I eliminate premultipliers of "1." ?
  • From: "Alan Mason" <swt at austin.rr.com>
  • Date: Sun, 14 Oct 2001 04:11:56 -0400 (EDT)
  • References: <9q8oeb$co$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hello Brett.
You can get rid of them by applying a rule.

In[9]:=
expr = 1.0 a

Out[9]=
1. a

In[10]:=
expr2 = expr /. 1.0 u_:> u

Out[10]=
a

..  I agree with you, though.  Mathematica 4.1 even claims that 1.0 == 1 is
True.
In[5]:=
1.0 \[Equal] 1

Out[5]=
True

I consider this an outright error. 1.0 means a floating-point approximation
to 1, whereas 1 is exactly 1

The correct way to treat 1.0/1.0 is somewhat ambiguous.  Does 1.0 stand for
the same approximation at each appearance?  If so, the ratio should be 1;
otherwise, it should be 1.0.

Alan

"Brett Patterson" <bap at roe.ac.uk> wrote in message
news:9q8oeb$co$1 at smc.vnet.net...
> Consider the following:
>
> In[1] := 1 a / 1
> Out[1] := a
>
> In[2] := 1.0 a / 1.0
> Out[2] := 1. a
>
> Now consider these identities:
>
> In[3] := (1 / 1) == 1
> Out[3] := True
>
> In[4] := (1.0 / 1.0) == 1.0
> Out[4] := True
>
> In[5] := (1 / 1) == 1.0
> Out[5] := True
>
> In[6] := (1.0 / 1.0) == 1
> Out[6] := True
>
> Given that it is clear mathematically that I want the
> answer to In[2] to evaluate to just "a", and given that
> Mathematica is clearly recognizing that 1.0 / 1.0 is the
> same as 1 / 1, can someone please tell me why Out[2] contains
> the premultiplier "1." and how to eliminate it in expressions
> that might contain this superfluous unit multiplier in various places.
>
> Thanks!
>
> Brett Patterson
>
> UK Astronomy Technology Centre
> The Royal Observatory
> Blackford Hill
> Edinburgh EH9 3HJ
> Scotland
>



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