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Re: Zero times a variable in numerical calculations

• To: mathgroup at smc.vnet.net
• Subject: [mg68365] Re: Zero times a variable in numerical calculations
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Thu, 3 Aug 2006 06:06:22 -0400 (EDT)
• Reply-to: hanlonr at cox.net
• Sender: owner-wri-mathgroup at wolfram.com

Use Rationalize

0.0 * a // Rationalize

0


Bob Hanlon

---- 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
> 
> 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