Thank you for your answer and sorry for the typo mistake.
Your solution works well with the example given but doesn't work as I would
like with exponents (x^2, ...).
What I would like to get is Sage returning expressions with coefficients
sorted by the value of the exponents, like when using multivariate
polynomial rings.
Here is an example :
*****************************
var('x y z A B')
f = (1+B*(x+y))^((B-1)/(2*B)) * exp(z/2) / (1+(x-y)/A)
f = taylor(f,(x,0),(y,0),(z,0),2)
#this definition of a polynomial ring is useless
R.<A,B> = QQ[]
R.<x,y,z> = PolynomialRing(QQ[A,B],order='deglex')
print f
*****************************
I want to sort the terms of a polynomial obtained with a Taylor expansion.
I cannot declare a polynomial ring to have the terms automatically sorted
because the initial expression is not a polynomial. I tried to ask Sage to
switch to a polynomial ring after applying the Taylor expansion, but it
doesn't change anyting.
What I would like to obtain is the following answer (I copied/pasted the
solution of the Taylor expansion and I worked in a polynomial ring) :
*****************************
R.<A,B> = QQ[]
R.<x,y,z> = PolynomialRing(QQ[A,B],order='deglex')
f = 1/2*(((B - 1)*A - 2)*x + ((B - 1)*A + 2)*y + A*z)/A + 1/8*(A^2*z^2 -
((B^2 - 1)*A^2 - 4*(B - 1)*A - 8)*y^2 - ((B^2 - 1)*A^2 + 4*(B - 1)*A -
8)*x^2 + 2*((B - 1)*A^2 + 2*A)*y*z - 2*(((B^2 - 1)*A^2 + 8)*y - ((B -
1)*A^2 - 2*A)*z)*x)/A^2 + 1
print f
*****************************
Is there a solution to my problem ?
Thanks
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