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MathGroup Archive 1997

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Re: How to define an auto-Collect function (fwd)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7750] Re: How to define an auto-Collect function (fwd)
  • From: "C. Woll" <carlw at u.washington.edu>
  • Date: Mon, 7 Jul 1997 04:41:21 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

On Thu, 3 Jul 1997, Roland Franzius wrote:

> just define
> prd/: prd[a_,b_]+prd[a_,c]:=prd[a,b+c]
> Your example takes 1.9 s on my old 486dx2/66
> r.franzius
> 

Hi Roland,

Thanks for the input on my question. Unfortunately, I think you might have
made a mistake. First, there is no difference between the statements

prd /: prd[a_,b_]+prd[a_,c_]:=prd[a,b+c]

and

prd[a_,b_]+prd[a_,c_]^:=prd[a,b+c]

Try out both statements and check ??prd. Secondly, I think you might have
missed the underscore after the c in the second prd. Without the
underscore, the collecting function won't work, and my example will not
work. As a test of your definition, make sure that 

prd[x,y]+prd[x,z]

returns 

prd[x,y+z]

Note that without the underscore, my example will run much faster, since
there is less generality in the prd definition.

Again, thanks for your suggestion.

Carl Woll





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