Re: Extracting polynomial coefficients?
- To: mathgroup@smc.vnet.net
- Subject: [mg11509] Re: [mg11464] Extracting polynomial coefficients?
- From: "C. Woll" <carlw@u.washington.edu>
- Date: Fri, 13 Mar 1998 12:21:59 -0500
Hi Tom,
Here is one idea, and I am sure that there are many more. If expr is
your expression, then try
Expand[Collect[expr,{a,b,c,d},g]] /. x_ g[y_] :> Print[x " => " y];
The main idea is to use Collect. The function g is just a dummy head
which prevents the argument from being expanded when the collected
expression is expanded, and the final rule causes Mathematica to print
out the expressions you wanted.
Note that you could also replace " => " with :esc:=>:esc: where :esc: is
the escape key. That is
Print[x :esc:=>:esc: y]
Happy computing!
Carl Woll
Dept of Physics
U of Washington
On Thu, 12 Mar 1998, Thomas Bell wrote:
> I have a very long polynomial that's a function of four variables, a, b,
> c, d. I would like Mathematica to (1) tell me what combinations of a,
> b, c, and d are in my polynomial, and (2) tell me what the coefficients
> are for each of the variable terms.
>
> For example, say I have constant terms r and q. My polynomial might
> look something like
>
> 4 a^2 b^3 c + r q d^5 + a d^3 + q c^2 a^2 + r^2 a d^3
>
> I would like to have Mathematica output something like:
>
> a^2 b^3 => 4
> d^5 => r q
> a d^3 => 1 + r^2
> c^2 a^2 => q
>
> The polynomial is long enough that it would be very time-consuming to
> search through and identify all the combinations of (a,b,c,d).
>
> Any help appreciated. Thanks.
>
> -------------------------------------------------------------- Thomas
> (Tom) Bell Gravity Probe-B, H.E.P.L. tombell@stanford.edu Stanford
> University 136D Escondido Village Stanford, CA 94305-4085 Stanford, CA
> 94305 650/725-6378 (o) 650/497-4230 (h) 650/725-8312 (fax)
>
>