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Re: Applying restrictions on matrix multiplication


Hi,

One way to have Mathematica automatically set products to zero is to use
upvalues. For example, if you wanted products of expressions with the
head z to be set to zero, you could use the rule

z /: a_z b_z := 0

A slight problem in your case is that you are working with subscripts,
and so you can't associate the upvalues with E as E is too deep. So,
you will need to associate upvalues with Subscript instead, as in

Subscript /: Subscript[E,_] Subscript[E,_] := 0

Instead of the above rule, you could of course write out the rule using
2-D syntax.

Carl Woll
Dept of Physics
U of Washington

On 1 Aug 1998, Van Graves wrote:

> I need some help applying restrictions on multiplying two matrices
> within Mathematica.  The elements contain expressions of Ex, Ey, Ez
> (where E=greek letter sigma and the xyz are subscripts).  In these
> matrices, the E terms are assumed to be nearly zero, so I would like to
> throw out any terms where two or more E's are multiplied together, thus
> simplifying the resultant matrix before applying it with another one
> (these are transformation matrices).
> 
> If T01 and T12 are two 4x4 matrices, can I somehow place a restriction
> on T01.T12 to get a simplified result?  Or can I simplify the result
> after it's calculated?
> 
> Thanks for any help.
> 
> ***********
> Van Graves
> Oak Ridge National Laboratory          gravesvb at ornl.gov University of
> Tennessee                vgraves at utk.edu ***********
> 
> 
> 



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