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MathGroup Archive 2006

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Modify a list of pure functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70812] Modify a list of pure functions
  • From: "." <ggroup at sarj.ca>
  • Date: Sat, 28 Oct 2006 05:21:54 -0400 (EDT)

Hi all,

I have a problem where I need to build up a list of pure functions that
have been modified from a base pure function.  I'm not having much luck
in getting it to work correctly, and was wondering if anyone had some
good ideas.  A toy version of the problem is:

f = Sin[#]&
listF = Table[(i f[##])&, {i, 5}]

What I'd hope to get is listF containing:
{Sin[##]&, (2 Sin[##])&, (3 Sin[##])&, (4 Sin[##])&, (5 Sin[##])&}

But instead, I get something where neither i nor f have been evaluated.
 As I say, this is a toy example.  One thing that does partially work
for the toy case, but does not seem to work for more complicated
situations is to use ReplaceAll:

listF2 = Table[{j f[##])& /. j->i, {i,5}]

This does give:
{1 f[##1] &, 2 f[##1] &, 3 f[##1]&, 4 f[##1] &, 5 f[##1] &}

However, all that has been done is the index has been inserted; no
significant evaluation seems to have occurred.  So this method doesn't
work in more complicated situations.  For example, suppose insted of
using the index i directly, it actually referred to a list:

coeffs = Reverse[ Range[5] ];
listF3 = Table[ (coeffs[[j]] f[##]) & /. j->i, {i, 5}]

This just gives:
{coeffs[[1]]*f[##1] & , coeffs[[2]]*f[##1] & , coeffs[[3]]*f[##1] & ,
coeffs[[4]]*f[##1] & , coeffs[[5]]*f[##1] & }

Which is no good if coeffs is a temporary variable.

Any suggestions would be most appreciated.  Thanks!


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