Re: Solve's Strange Output

*To*: mathgroup at smc.vnet.net*Subject*: [mg89093] Re: Solve's Strange Output*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Sun, 25 May 2008 06:26:28 -0400 (EDT)*References*: <200805250604.CAA15590@smc.vnet.net>

On 25 May 2008, at 15:04, Bruce Colletti wrote: > Re 6.0.2 under WinXP. > > This code's output is strange: what does 0.-7.9424 g mean? Ditto > for all values returned by Solve. > > Thankx. > > Bruce > > > {x[0],y[0]}={10.5,6.08}; > {x[1],y[1]}={3.23,14.4}; > {x[2],y[2]}={18,12.7}; > m=16.1; > > Solve[{a+c==0,b+d==m*g,d(x[2]-x[0])==c(y[2]-y[0]),a(y[1]- > y[0])==b(x[1]-x[0])},{a,b,c,d}] > > Out[11]= {{a->0.-7.9424 g,b->0.+9.08951 g,c->0.+7.9424 g,d- > >0.+7.01049 g}} > 0. is just machine precision (hence approximate) 0, and In particular, for an undefined symbols a an approximate 0 does not behave like genuine 0: 0. + a a + 0. 0.*a 0. a This is reasonable since 0. + a could not be a, as Precision[0. + a] MachinePrecision while Precision[a] Infinity Andrzej Kozlowski

**References**:**Solve's Strange Output***From:*Bruce Colletti <bwcolletti@verizon.net>