       Re: How to simplify certain covariance expressions using

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• 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?

```

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