Re: Simplifying {0,0,0}.X.{0,0,0}
- To: mathgroup at smc.vnet.net
- Subject: [mg74028] Re: Simplifying {0,0,0}.X.{0,0,0}
- From: newsmetrohm <dh at metrohm.ch>
- Date: Wed, 7 Mar 2007 03:05:28 -0500 (EST)
- References: <esjg5a$26q$1@smc.vnet.net>
Hi Will,
simply efine two rules for X:
X/: {0,0,0}.X=0;
X/: X.{0,0,0}=0
Daniel
Will Robertson wrote:
> Hello,
>
> In brief: Is there a way that I can specify that "X" is a matrix and
> will resolve to zero when dot multiplied with a vector of zeros?
>
> I'm constructing a swathe of expressions that contain things like
> (when expanded): {0,0,0}.X.{0,0,0}, where X is an arbitrary (well,
> positive definite) square matrix of obvious size, and I'd like to be
> able to have mathematica simplify that for me without much
> intervention.
>
> My only option at the moment is to manually perform the replacements
> {{0, 0, 0}.X._ -> 0, _.X.{0, 0, 0} -> 0} (the left and right vectors
> won't always both be zeros), but this is tedious to perform for a
> large number of expressions. I could also define the matrix X in terms
> of its indices and end up with expressions in terms of x11, x12, ... ,
> x33, but I'd rather not do that.
>
> Any help would be greatly appreciated.
>
> Many thanks in advance,
> Will Robertson
>
>