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Re: combinations of pure functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg16598] Re: [mg16532] combinations of pure functions
  • From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
  • Date: Wed, 17 Mar 1999 23:55:05 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

Gianluca:

Just one more adition to my previous answer to your question. If for some
reason you do not like to add new global rules  you can of course do this:

In[1]:=
op = Identity - (D[#,x]&)
Out[1]=
Identity - (D[#1, x] & )

In[2]:=
Through[op[x^2],Plus]/.(-f_)[x_]->-(f[x])
Out[2]=
        2
-2 x + x

Andrzej


On Tue, Mar 16, 1999, Gianluca Gorni <gorni at dimi.uniud.it> wrote:


>Hello!
>
>Talking of operators, consider the example of the Book
>at Section 2.2.9:
>
>   op = Identity + (D[#,x]&)
>
>To find the value of op on the expression x^2 it is
>suggested to use Through:
>
>  Through[op[x^2], Plus]
>
>Unfortunately the suggestion fails if we just change +
>into - in op:
>
>   op2 = Identity - (D[#,x]&)
>
>What can one do? I have thought of a replacement rule:
>
>   op2 /. {Identity -> x^2, f_Function -> f[x^2] }
>
>Anyone has a better idea?
>
>Thank you in advance,
>
>                       Gianluca Gorni
>
>
> +---------------------------------+
> | Gianluca Gorni                  |
> | Universita` di Udine            |
> | Dipartimento di Matematica      |
> |   e Informatica                 |
> | via delle Scienze 208           |
> | I-33100 Udine UD                |
> | Italy                           |
> +---------------------------------+
> | Ph.: (39) 0432-558422           |
> | Fax: (39) 0432-558499           |
> | mailto:gorni at dimi.uniud.it      |
> | http://www.dimi.uniud.it/~gorni |
> +---------------------------------+
>
>
>


Andrzej Kozlowski
Toyama International University
JAPAN
http://sigma.tuins.ac.jp/
http://eri2.tuins.ac.jp/



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