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combinations of pure functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg16532] combinations of pure functions
  • From: Gianluca Gorni <gorni at dimi.uniud.it>
  • Date: Tue, 16 Mar 1999 04:00:09 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

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


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