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Re: Approximate Zero Times A Symbol

  • To: mathgroup at smc.vnet.net
  • Subject: [mg127072] Re: Approximate Zero Times A Symbol
  • From: Christoph Lhotka <christoph.lhotka at fundp.ac.be>
  • Date: Thu, 28 Jun 2012 04:02:43 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201206270811.EAA18698@smc.vnet.net>

Hello,

My argumentation would be as follows:

  0 x = 0  if (0,x) have infinite precision, while 0. x = 0. since the 
result has a precision at most of 0.,
therefore there is no need to keep the x, which has infinite precision: 
for the expression we only
need x up to precision of 0., therefore 0. * approximate x = 0., which 
is true up to the precision
of 0.

If I understand well, what you would like to have and if it only 
concerns the format it is printed,
I would define:

dis[ex_]:=Plus@@({x,y}*(StringTrim/@ToString/@(PaddedForm[Coefficient[ex,#],{8,8}]&/@{x,y})))

which would give

dis/@{0.x+1.y,0.34324324324324324324324x+1.000000000004y}
{0.00000000 x+1.00000000 y,0.34324324 x+1.00000000 y}

Hope that helps,

   Christoph


On 06/27/2012 10:11 AM, djmpark wrote:
> What is the justification for the following?
>
>
>
> 0. x + 1. y
>
>
>
> 0. + 1. y
>
>
>
> I want to display a dynamic weighted sum of x and y and sometimes one of the
> coefficients becomes zero. I would like to keep both terms (for a steady
> display) and format with NumberForm.  If Mathematica is going to drop the x,
> why doesn't it at least also drop the approximate zero?
>
>
>
> If I use SetPrecision we obtain:
>
>
>
> SetPrecision[0. x + 1. y, 10]
>
>
>
> 1.000000000 y
>
>
>
> which is at least more consistent, but not what I want either.
>
>
>
> David Park
>
> djmpark at comcast.net
>
> http://home.comcast.net/~djmpark/index.html
>




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