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Re: keep special functions unexpanded

  • To: mathgroup at smc.vnet.net
  • Subject: [mg131415] Re: keep special functions unexpanded
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Sun, 21 Jul 2013 04:23:37 -0400 (EDT)
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t = Table[
  {ChebyshevT[ToString[i], x], ChebyshevT[i, x]},
  {i, 0, 2}]


{{ChebyshevT["0", x], 1},
   {ChebyshevT["1", x], x},
   {ChebyshevT["2", x], -1 + 2*x^2}}


t /. i_String :> ToExpression[i]


{{1, 1}, {x, x}, {-1 + 2*x^2, -1 + 2*x^2}}



Bob Hanlon




On Sat, Jul 20, 2013 at 5:58 AM, metrologuy <takacs at bnl.gov> wrote:

> I am trying to create a list of ChebyshevT[n,x] polynomials of different
> orders to use as basis functions in a fitting routine. I want to keep the
> list in the form that explicitly shows the order number. For example, I
> want the list for order n=2 to look like this:
>   basislist={ChebyshevT[0,x],ChebyshevT[1,x],ChebyshevT[2,x]}.
> If I use Table to generate the list, I get each function expanded into a
> polynomial in x:
>
> In[1]:= Table[ChebyshevT[i,x],{i,0,2}]
>
> Out[1]= {1,x,-1+2 x^2}
>
> How can I prevent the function from displaying the expanded form for each
> value of n? If I use the unexpanded form in the Fit[] function, it works
> just fine. But I lose the visual connection to the explicit order number in
> the input form of the function. Any suggestions how to keep the "n" visible?
>
>



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