First of all, thank you for your quick response.
I think it is better if I explain the problem a little bit more:
At the moment I have a (differential) equation that consists of several
terms in a sum; the equation is Navier-Stokes-ish.
A few terms have to be dropped according to order of magnitude analysis.
For this reason the combination c1*(1 - a*b) is expanded to c1 - c1*a*b;
the term c1*a*b might be dropped only...
Now, the problem is that when the c1*a*b term is *not *dropped, it is
preferable to factor the sum c1 - c1*a*b back to the form c1*(1 - a*b).
Note that c1 is unknown, one really has to use the combination (1 - a*b) to
perform the factorization.
The commands *collectterms *and *facsum* with the argument (1 - a*b) do not
solve this problem...
I have reasons to believe that only single variables can be supplied as an
argument to these commands.
The question remains, how can this be handled otherwise?
Kind regards,
Koen Groot
2012/10/24 Barton Willis <willisb at unk.edu>
>
> > In deriving so called ``Parabolized Stability Equations" for fluid
> mechanic stability, I like to factor an expression like (1 - a*b).
>
> I'm not sure what you mean by factoring 1 - a * b, but one possibility
> might be to use substitution--something like
> subst(XXX, 1-a*b, YYY) or maybe ratsubst(XXX,1-a*b, YYY) .
>
> --Barton
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