Re: Convert expression to polynomial
- To: mathgroup at smc.vnet.net
- Subject: [mg70412] Re: Convert expression to polynomial
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Mon, 16 Oct 2006 02:33:57 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <egsd96$cj7$1@smc.vnet.net>
Diana wrote:
> Math folks,
>
> I am generating a list of partial sums which look like:
>
> x = 1 + (-t + t^2)^(-1) + 1/((-t + t^2)^2*(-t + t^4)) + 1/((-t +
> t^2)^4*(-t + t^4)^2*(-t + t^8))
>
> I then try to calculate the PolynomialQuotient[Numerator[x],
> Denominator[x], t], etc., and I get an error saying that x is not a
> polynomial function.
>
> I tried to find the command to put everything over a common
> denominator, but was unable to find this. Can someone help?
>
> Thanks,
>
> Diana M.
>
Hi Diana,
Use the built-in function Together [1].
In[1]:=
x = 1 + (-t + t^2)^(-1) +
1/((-t + t^2)^2*(-t + t^4)) +
1/((-t + t^2)^4*(-t + t^4)^2*(-t + t^8))
Out[1]=
1 1
1 + ------- + -------------------- +
2 2 2 4
-t + t (-t + t ) (-t + t )
1
-------------------------------
2 4 4 2 8
(-t + t ) (-t + t ) (-t + t )
In[2]:=
Together[x]
Out[2]=
4 5 6 7 8 9
(1 + t - 2 t + 2 t - 5 t + 9 t - 10 t +
10 11 12 13 14
12 t - 16 t + 17 t - 14 t + 14 t -
15 16 17 18 19
16 t + 14 t - 13 t + 15 t - 15 t +
20 21 22 23 24
12 t - 9 t + 7 t - 4 t + t ) /
7 7 2 2
((-1 + t) t (1 + t + t )
2 3 4 5 6
(1 + t + t + t + t + t + t ))
In[3]:=
PolynomialQuotient[Numerator[Together[x]],
Denominator[Together[x]], t]
Out[3]=
1
Regards,
Jean-Marc
[1] http://documents.wolfram.com/mathematica/functions/Together