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Re: How to simplify certain covariance expressions using

• To: mathgroup at smc.vnet.net
• Subject: [mg128038] Re: How to simplify certain covariance expressions using
• From: Barrie Stokes <Barrie.Stokes at newcastle.edu.au>
• Date: Mon, 10 Sep 2012 04:06:00 -0400 (EDT)
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• References: <20120909213324.167C06765@smc.vnet.net>

Hi

cov = ((ea + ex) (ea + ey) // Expand) /. {ex ey -> 0, ey ex -> 0}

Barrie

>>> On 10/09/2012 at 7:33 am, in message <20120909213324.167C06765 at smc.vnet.net>,
<hewei2004 at gmail.com> wrote:
> Hi,
> 
>   I have a certain case of covariance to simplify. 
> 
> Suppose I have the following expression:
> cov=(ea+ex)(ea+ey)=eaea+eaex+eaey+exey
> 
> How can I assume that whenever ex times ey ,the product is 0, so that the 
> expression I want to get out of is
> 
> Assuming[exey=0,Refine[cov]]=eaea+eaex+eaey
> So that the last term:exey, drops out. 
> 
> My problem is that the Assuming[] function won't take exey=0 as a valid 
> assumption. Is there any way to do this using some other function or I typed 
> something wrong?

• References:
  • How to simplify certain covariance expressions using
    • From: hewei2004@gmail.com