# [Maxima] Factorization problem

David Ronis ronis at ronispc.chem.mcgill.ca
Tue Jul 17 10:12:11 CDT 2012

```Hi Robert,

Thanks for the reply.   Actually, this is as "real" as it gets.  f (or
something close to it) is what I get after doing a messy 3 dimensional
integral, with a messy integrand, in maxima.  It arises in the
calculation of correlations in a perturbative analysis of a stochastic
PDE.   ansp is what I get after manually factoring/simplifying f, i.e.,
with pen and paper.   ansp is manually entering the result (I've
checked, and ansp-f will ultimately simplify to 0 using the f that
results from the integrals).

Regards,

David

On Tue, 2012-07-17 at 04:12 +0000, Robert Dodier wrote:
> On 2012-07-13, David Ronis <David.Ronis at McGill.CA> wrote:
>
> > Thanks for the suggestions; however none of them seem to really do the
> > trick.   Here's a real example:
> >
> > kill(all);
> > ansp: xi*((xi^2-k[0]^2)*log((abs(xi-k[0])/(xi+k[0]))^2)+4*k[0]*xi)
> > /(k[0]*(Gamma+D*(xi^2-k[0]^2)))
> >
> > *((exp(-D*k[0]^2*(t[0]+t[3]))-exp(-2*Gamma*t[3]-D*k[0]^2*(t[0]-t[3])))
> >      /(Gamma-D*k[0]^2)
> >      +(exp(-Gamma*(t[0]+t[3])-D*xi^2*(t[0]-t[3]))
> >        +exp(-2*Gamma*t[3]-D*k[0]^2*(t[0]-t[3]))
> >        -exp(-D*k[0]^2*t[3]-(D*xi^2+Gamma)*t[0])
> >        -exp(-(Gamma+D*xi^2)*t[3]-D*k[0]^2*t[0]))/(Gamma-D*(xi^2+k[0]^2))
> >      );
> >
> > f:ratsimp(%);
>
> Well, how real is it? Is f something found in the wild? Doesn't seem to
> be, since f is constructed as ratsimp(ansp). It makes a difference in
> this case since ratsimp rearranges the expression so that the exponents
> are different, which means that reconstructing the original ansp from f
> cannot be carried out by considering exponents alone.
>
> But that may well be beside the point. What are some expressions which
> you have actually encountered?
>
> best
>
> Robert Dodier
>
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```