Re: Efficient use of coefficient--Efficient simplification
- To: mathgroup@smc.vnet.net
- Subject: [mg11195] Re: [mg11183] Efficient use of coefficient--Efficient simplification
- From: "C. Woll" <carlw@u.washington.edu>
- Date: Mon, 2 Mar 1998 23:10:50 -0500
Hi Joel,
One way to do what you want is to use Collect:
Collect[ expr , ket[_] ]
where expr is the expression you want to simplify. However, I don't know
if this works in Mathematica 2.2.
Carl Woll
Dept of Physics
U of Washington
On Wed, 25 Feb 1998, Joel Cannon wrote:
> I wish to simplify expressions such as the following which possess terms
> involving ket[n+i]. They involve a variable range of indices i.
>
> Out[164]=
> -(Sqrt[n] (Sqrt[-1 + n] ket[-2 + n] - Sqrt[n] ket[n])) +
>
> Sqrt[1 + n] (Sqrt[1 + n] ket[n] - Sqrt[2 + n] ket[2 + n])
>
> I can collect the various terms in ket[n+i] with the following
> operation:
>
> In[176]:=
> Out[164]//Expand// Table[ket[n+i] Coefficient[#,ket[n+i] ],{i,-2,2}]&
> //Plus @@ #&
>
> Out[176]=
> -(Sqrt[-1 + n] Sqrt[n] ket[-2 + n]) + (1 + 2 n) ket[n] -
>
> Sqrt[1 + n] Sqrt[2 + n] ket[2 + n]
>
> My problem is this, Since I do no know what the range of ket[n+i] will
> be, I would like to write a general expression that will find what
> ket[n+i] are present and collect the coefficients of each of these. The
> inelegant wat is to run over a range of i's that will surely bracket
> any ket[n+i] that I will possibly encounter, but that is distasteful.
> I am using version 2.2 but will probably switch to 3.0 soon.
>
> Any other suggestions to that way I have done things are welcomed. If
> possible, please copy me on email since I might otherwise miss posts to
> the newsgroup.
>
> cannon@alpha.centenary.edu
>
> Thanks very much,
>
> ------------------------------------------------------------------------------
> Joel W. Cannon | (318)869-5160 Dept. of
> Physics | (318)869-5026 FAX Centenary College of
> Louisiana | P. O. Box 41188 |
> Shreveport, LA 71134-1188 |
>
>