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Re: Approximate Zero Times A Symbol

  • To: mathgroup at smc.vnet.net
  • Subject: [mg127075] Re: Approximate Zero Times A Symbol
  • From: "djmpark" <djmpark at comcast.net>
  • Date: Thu, 28 Jun 2012 04:03:45 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201206270811.EAA18698@smc.vnet.net> <7170720.3259.1340794919180.JavaMail.root@m06>

Thanks Bob, but I think I didn't express myself clearly enough. What I have
is a dynamic display where the coefficients are varied and I want to retain
x and y in the display even when their coefficients are zero.

The following is what I ended up doing, but it does seem like a roundabout
method to obtain the result.

angle = 0.;
Slider[Dynamic[angle], {0., 90.}, Appearance -> "Labeled"]
Dynamic@NumberForm[
  HoldForm[aa x + bb y] /.
    Thread[{aa, bb} -> {Sin[angle Degree], Cos[angle Degree]}] //
   Chop, {7, 6}]

And I still don't understand why Mathematica should drop the x if x is not a
numeric quantity.

David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/index.html




From: Bob Hanlon [mailto:hanlonr357 at gmail.com]


Use Rationalize

expr = 0. x + 1. y;

expr // Rationalize

y

expr // Rationalize[#, 0] &

y

If there are any rational factors remaining you can use N with any desired
precision to return to reals.


Bob Hanlon


On Wed, Jun 27, 2012 at 4:11 AM, djmpark <djmpark at comcast.net> 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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