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Ugly Trig Mess

• To: mathgroup at smc.vnet.net
• Subject: [mg13212] Ugly Trig Mess
• From: Tobias Oed <tobias at physics.odu.edu>
• Date: Mon, 13 Jul 1998 07:43:00 -0400
• Organization: Old Dominion University
• Sender: owner-wri-mathgroup at wolfram.com

Hi all,

In a calculation I am doing I end up with a long sum of terms (~3000) of
the form:

f1 a.b + f2 a.Cross[b,c] + f4 a.d b.Cross[a,c] + f5 ...

Where a,b,c,d represent vectors (In my problem there are 6 of them,
forming 
about 500 structures like a.Cross[b,c])

I would like to find a clever algorithm that uses the relations

a.Cross[b,c]=b.Cross[c,a]=c.Cross[a,b]

Cross[a,Cross[b,c]]= (a.c) b - (a.c) b

Cross[a.b] Cross[c.d] = a.c b.d - a.d b.c

in order to rewrite some of the structures as sums of other  structures.
I have thought of something recursive but my computer  runs out of
memory.

any help is welcome, Tobias