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)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*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