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Re: Zero times a variable in numerical calculations

• To: mathgroup at smc.vnet.net
• Subject: [mg68396] Re: Zero times a variable in numerical calculations
• From: "Chris Chiasson" <chris at chiasson.name>
• Date: Thu, 3 Aug 2006 06:07:29 -0400 (EDT)
• References: <A56895C7CA4FC73.5FEF25D660@comcast.net> <001a01c6b610$89380640$69425f86@haverkort>
• Sender: owner-wri-mathgroup at wolfram.com

I guess this happens because you are using inexact numbers.

Try using exact numbers or use Chop.

On 8/2/06, Maurits Haverkort <Haverkort at ph2.uni-koeln.de> wrote:
>
>
>
>
> Dear All
>
>
>
> I have the following problem.
>
> In: 0.0 a
>
> Out 0. a
>
>
>
> I would like to have that
>
> In: 0.0 a
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> Simplifies to
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> Out: 0
>
>
>
> SetPrecision[0.0 a,10^-100] works, but I am a bit puzzled
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>
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> 0.0 ==0 returns true
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> 0.0 a == 0 a returns unevaluated to 0.0 a == 0
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>
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> This seems inconsistent to me.
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>
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> 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


-- 
http://chris.chiasson.name/