Dear William, Dear Waldek,
many thanks for your help!
I guess, the real problem is that
(71) -> ex :=
((-2*t*x*y)+(-2*t*x^2))/(y*(t^2*y^4+((-4*t^2)+(-2*t))*x*y^3+((-6*t^2)+1)*x^2*y^2+((-4*t^2)+(-2*t))*x^3*y+t^2*x^4)^(1/2)+t*y^3+(-x*y^2)+t*x^2*y)
2
- 2t x y - 2t x
(71)
--------------------------------------------------------------------------------------------
+------------------------------------------------------------------+
| 2 4 2 3 2 2 2 2 3 2 4
3 2 2
y\|t y + (- 4t - 2t)x y + (- 6t + 1)x y + (- 4t - 2t)x y + t x
+ t y - x y + t x y
Type: Expression Integer
(72) -> series(ex, t=0)
2 3 2 2 3
- 2x y - 2x - 2y - 2x y - 2x y - 2x 2 3
(72) --------------- t + -------------------------- t + O(t )
+----+ +----+
| 2 2 2 2 | 2 2 3
y\|x y - x y y \|x y - x y
Type:
UnivariatePuiseuxSeries(Expression Integer,t,0)
is not correct in general, eg., when x*y > 0. In my case, I consider x and y
in fact as formal power series in t themselves, and I think I also want that
sqrt(x^2)=x.
Martin
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