function for regrouping/factoring the following expression
Subject: function for regrouping/factoring the following expression
From: Rupert Swarbrick
Date: Sun, 25 Jul 2010 22:10:37 +0100
R Fateman <fateman at cs.berkeley.edu> writes:
> On 7/25/2010 1:11 PM, Julien Martin wrote:
>> Hello,
>> I would like to find the Maxima function for isolating the x^3, x^2,
>> x in say, the following expression:
>> A*x^2 + B*x^3 -2*B*x^2 +A*x-5*B*x+3*B
>> So that I have (A-2*B)*x^2 etc... with x^3, x^2 and x appearing only
>> once in the resulting expression.
>
> try rat(...,X);
As Richard Fateman said, but if you want to actually get the
coefficients, use the coeff function afterwards:
(%i1) A*x^2 + B*x^3 - 2*B*x^2 + A*x - 5*B*x + 3*B;
3 2 2
(%o1) x B - 2 x B - 5 x B + 3 B + x A + x A
(%i2) rat(%, x);
3 2
(%o2)/R/ B x + (- 2 B + A) x + (- 5 B + A) x + 3 B
(%i3) coeff(%o2, x, 3);
(%o3)/R/ B
(%i4) coeff(%o2, x, 2);
(%o4)/R/ - 2 B + A
(%i5) coeff(%o2, x, 1);
(%o5)/R/ - 5 B + A
(%i6) coeff(%o2, x, 0);
(%o6)/R/ 3 B
(%i7)
(note that coeff doesn't do anything _that_ clever, so if your power
of x isn't explicit, it won't work:
(%i7) coeff( (x+2)^500, x, 3);
(%o7) 0
which is why it's always a good idea to make sure everything's fully
expanded in terms of x first)
Rupert
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