How to discard negative solutions
- To: mathgroup at smc.vnet.net
- Subject: [mg129309] How to discard negative solutions
- From: "Dr. Robert Kragler" <kragler at hs-weingarten.de>
- Date: Mon, 31 Dec 2012 19:45:51 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- Delivered-to: l-mathgroup@wolfram.com
- Delivered-to: mathgroup-newout@smc.vnet.net
- Delivered-to: mathgroup-newsend@smc.vnet.net
- Reply-to: kragler at hs-weingarten.de
Hi,
from a geometric problem I obtain with $Assumptions = {a > 0, b > 0, c > 0}
using Solve a series of solutions such as
{b -> a, c -> a} but also {c -> -a - b}.
The latter one should obviously be discarded because it will be negative
according to the assumptions (a>0, b>0) above.
How can these negative solutions being excluded by Mathematica V8 ? Positve[]
and NonNegative[] do not help because quantities which are not NumericQ remain
unevaluated. Help is appreciated.
Robert Kragler