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:
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 > > email@example.com > > http://home.comcast.net/~djmpark/index.html >