• 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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