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>
- Solve's Strange Output