thank you very much for your prompt answer and sorry for not
describing my problem sufficiently.
i thinking about maxima as a tool to generate analytical derivatives
into my optimization program. i have hundreds of similar expressions
and i want this to be a part of general simplification method which
will be called over each of the expressions.
so i don't know in advance if there will be some (b^2+a^2)
subexpression. but if there will be i would like to handle them as i
described.
the command "substpart(factor(piece),e1,[1,4]);" is based on knowledge
the (b^2+a^2) subexpressions are at positions 1 and 4. i think i'm
looking for some content based method for this - if there are some
(b^2+a^2) subexpressions then factor them out.
thank you very much
vit mach-zizka
2011/12/19 Stavros Macrakis <macrakis at alum.mit.edu>:
> Don't know if this counts as "elegant", but...
>
> (%i1) exp: a^2*gama+b^2*gama + beta*a*c*p + beta*b*d*p - c*b*gama*p +
> a*d*gama*p - beta*c*b*r + beta*a*d*r - a*c*gama*r - b*d*gama*r +
> a^2*G+b^2*G;
> (%o1) b^2*G+a^2*G-b*d*gama*r-a*c*gama*r+a*beta*d*r-b*beta*c*r+a*d*gama*p
> ? ? ? ? ? ?-b*c*gama*p+b*beta*d*p+a*beta*c*p+b^2*gama+a^2*gama
> (%i2) e1:facsum(exp,r,p,[gama,beta]);
> (%o2) (b^2+a^2)*G+(beta*(a*d-b*c)-(b*d+a*c)*gama)*r
> ? ? ? ? ? ? ? ? ?+((a*d-b*c)*gama+beta*(b*d+a*c))*p+(b^2+a^2)*gama
> (%i3) e2:substpart(factor(piece),e1,[1,4]);
> (%o3) (b^2+a^2)*(G+gama)+(beta*(a*d-b*c)-(b*d+a*c)*gama)*r
> ? ? ? ? ? ? ? ? ? ? ? ? +((a*d-b*c)*gama+beta*(b*d+a*c))*p
>
>
> 2011/12/19 V?t Mach-?i?ka <vit.machzizka at gmail.com>
>>
>> exp: a^2*gama+b^2*gama + beta*a*c*p + beta*b*d*p - c*b*gama*p +
>> a*d*gama*p - beta*c*b*r + beta*a*d*r - a*c*gama*r - b*d*gama*r +
>> a^2*G+b^2*G;
>
>