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MathGroup Archive 1997

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Q: About constants inside Distribute

  • To: mathgroup at smc.vnet.net
  • Subject: [mg9187] Q: About constants inside Distribute
  • From: sergio at scisun.sci.ccny.cuny.edu (Sergio Rojas)
  • Date: Tue, 21 Oct 1997 02:03:01 -0400
  • Organization: City College Of New York - Science
  • Sender: owner-wri-mathgroup at wolfram.com

Hi guys,

  	The rule:

        	rule = Dot[s___,(k:(a[i_]))m___, r___]:> k Dot[s,m,r]

       works fine separating constants (a[i_]) in the distribution of
       a Dot product:

        	f = O1*a[1] + O2*a[2]
        	g = P1*a[3] 
        	h = O2*a[3] 

In[44]:= Distribute[f.g.h]//.rule

                  2                         2 Out[44]= a[1] a[3]  O1 .
P1 . O2 + a[2] a[3]  O2 . P1 . O2

       However, the rule does not work if product of constants (
a[i_]*a[j_] )
       are included. For example, taking:

        	g = P1*a[3]*a[1]

In[45]:=  g = P1*a[3]*a[1]

Out[45]= P1 a[1] a[3]

In[46]:= Distribute[f.g.h]//.rule

             2
Out[46]= a[1]  a[3] O1 . P1 . a[3] . O2 + a[1] a[2] a[3] O2 . P1 . a[3]
. O2


  After playing with this for a while ( a big one ), I was unable to 
figure out what is going on and how to fix it. Could anybody point out
some suggestions?

Salut,

Rojas
E-mail: sergio at scisun.sci.ccny.cuny.edu



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