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Analytic Solution != Numerical Solution

• To: mathgroup at smc.vnet.net
• Subject: [mg128418] Analytic Solution != Numerical Solution
• From: Dmitry Meyerson <dmitry.meyerson at gmail.com>
• Date: Thu, 18 Oct 2012 02:35:26 -0400 (EDT)
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• Delivered-to: l-mathgroup@wolfram.com
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Dear Group members,

I ran into a case where Mathematica Solve yields different solutions depending on whether I solve it analytically (and then plug in some numbers) or numerically. I'm solving an algebraic equation, with some square roots. Mathematica does NOT complain about branch cut or anything else when solving the problem analytically. Based on physical reasoning that created the equation in the 1st place the purely numerical solution is the correct one. I attached a 3-line pdf version of the notebook that demonstrates this issue. Thank you for any suggestions!

https://docs.google.com/file/d/0B8Jyg5K5AFrGSjhuempfSndqa3M/edit