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Zero times a variable in numerical calculations

• To: mathgroup at smc.vnet.net
• Subject: [mg68395] Zero times a variable in numerical calculations
• From: "Maurits Haverkort" <Haverkort at ph2.uni-koeln.de>
• Date: Thu, 3 Aug 2006 06:07:28 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

Dear All



I have the following problem.

In: 0.0 a

Out 0. a



I would like to have that

In: 0.0 a

Simplifies to

Out: 0



SetPrecision[0.0 a,10^-100] works, but I am a bit puzzled



0.0 ====0 returns true

0.0 a ==== 0 a returns unevaluated to 0.0 a ==== 0



This seems inconsistent to me.



1) Could anyone explain me the logic behind this?

2) What is the fastest way to multiply a numerical matrix times a half numerical half analytical sparse matrix, whereby the result is band diagonal. (The current result has 0. a + 0. b + 0. c + 0. d + 0. e + 0. f on all places where it should be zero.)



Thanks in advance.

Maurits Haverkort