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Topic: keep special functions unexpanded
Replies: 1   Last Post: Jul 21, 2013 4:14 AM

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Bob Hanlon

Posts: 906
Registered: 10/29/11
Re: keep special functions unexpanded
Posted: Jul 21, 2013 4:14 AM
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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 <> 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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