Re: Approximate Zero Times A Symbol

*To*: mathgroup at smc.vnet.net*Subject*: [mg127068] Re: Approximate Zero Times A Symbol*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Thu, 28 Jun 2012 04:01:20 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201206270811.EAA18698@smc.vnet.net>

Zero times anything is zero (Times help: "0 x evaluates to 0, and 0.0 x evaluates to 0.0."). For an extreme example, 0 * Plot[x, {x, 0, 1}] 0 Another approach: Manipulate[ theta = angle Degree; NumberForm[Row[{ Sin[theta], " ", x, " + ", Cos[theta], " ", y}] // Chop, {7, 6}], {{angle, 0, " angle\n{degrees)"}, 0, 90, 0.5, Appearance -> "Labeled"}] Bob Hanlon On Wed, Jun 27, 2012 at 12:25 PM, djmpark <djmpark at comcast.net> wrote: > 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 > -- Bob Hanlon

**References**:**Approximate Zero Times A Symbol***From:*"djmpark" <djmpark@comcast.net>