RE: Choose one solution in Mathematica
- To: mathgroup at smc.vnet.net
- Subject: [mg36116] RE: [mg36095] Choose one solution in Mathematica
- From: "David Park" <djmp at earthlink.net>
- Date: Thu, 22 Aug 2002 04:32:53 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Roberto,
One method is to use the Cases statement. Let's choose an equation that
actually has positive and negative solutions.
Solve[x^2 - 1 == 0, x]
Cases[%, HoldPattern[Rule[x, _?NonNegative]], \[Infinity]]
{{x -> -1}, {x -> 1}}
{x -> 1}
This was slightly tricky because the Cases statement has several forms, one
of which has a rule as the second argument. We don't intend that case, so we
have to put the rule pattern we are trying to match in a HoldPattern.
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
From: Roberto [mailto:roberto.de_santis at ecb.int]
To: mathgroup at smc.vnet.net
Dear all,
Assume that
x^2 - 2x + 1 = 0
The two solutions are x = -1 and x = 1.
If I assume that x > 0, then the only relevant solution would be x = 1.
How can I tell this to Mathematica?
Solve[x^2 - 2x + 1 = 0, x]
and then........
Many thanks.
Roberto De Santis