Re: Strange empty set of solutions
- To: mathgroup at smc.vnet.net
- Subject: [mg71814] Re: Strange empty set of solutions
- From: José Carlos Santos <jcsantos at fc.up.pt>
- Date: Thu, 30 Nov 2006 06:05:04 -0500 (EST)
- References: <ekh7pg$sgs$1@smc.vnet.net> <ekjfrf$d7h$1@smc.vnet.net>
On 29-11-2006 8:19, Jens-Peer Kuska wrote:
> and we can't read you mind and the memory of your computer
> so we must imagine a matrix M and write down
Do you want an example? Here it is:
M = {{4/5(c - 1), -2/Sqrt[5]s, 2/5(1 - c)},
{2/5(1 - c), -1 + s/Sqrt[5], 4/5 + c/5},
{-2s/Sqrt[5], -c, -1 + s/Sqrt[5]}} // N
with c = Cos[Sqrt[5]] and s = Sin[Sqrt[5]].
If I type
Solve[{M.{x, y, z} == {0, 0, 0}}, {x, y, z}]
I get
{{x -> 0. - 0.0438861 z, y -> 0. + 1. z}}
but if I type
Solve[{M.{x, y, z} == {0, 0, 0}, x^2 + y^2 + z^2 == 1}, {x, y, z}]
then I get the empty set. Why is that?
Best regards,
Jose Carlos Santos