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Re: Q: About constants inside Distribute
*To*: mathgroup at smc.vnet.net
*Subject*: [mg9230] Re: [mg9187] Q: About constants inside Distribute
*From*: "C. Woll" <carlw at u.washington.edu>
*Date*: Fri, 24 Oct 1997 01:00:45 -0400
*Sender*: owner-wri-mathgroup at wolfram.com
Hi Sergio,
I don't understand why you are using triple blanks instead of single
blanks. Here's how I would implement a solution for your problem using
rules:
rule = {(k_a m_) . s_ :> k m . s, m_ . (k_a s_) :> k m . s}
You could also write definitions for a or Dot, so that a[i_] extraction
and distribution were automatic. For example,
Unprotect[Dot];
Clear[Dot];
(a[i_]^n_. c_) . d_ := a[i]^n (c . d) c_ . (a[i_]^n_. d_) := a[i]^n (c .
d)
b_Plus . c_ := Distribute[Unevaluated[b . c]] b_ . c_Plus :=
Distribute[Unevaluated[b . c]]
Protect[Dot]
With the above f . g . h would automatically be put in the form you
want.
Good luck
Carl Woll
Dept of Physics
U of Washington
On Tue, 21 Oct 1997, Sergio Rojas wrote:
>
> 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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