- #1
l'Hôpital
- 258
- 0
So, I'm studying Dynamical Systems from Hirsch and Smale's "Differential Equations, Dynamical Systems, and Linear Algebra." For those who are acquainted with the book, the book is filled with typos. However, otherwise, it's great. I obtained this book from my University library and it appeared the reader before was very troubled by the typos and so he fixed most of them with pen/pencil. However, it seems the typo fixer got lazy a third of the way in, so I've kinda sort of fixed the errors I found. However, I'm currently stuck in one, that I'm just a little confused on whether it's an error or just a misunderstanding of mine. Straight from Hirsch and Smale:
Definition 1: Suppose [tex]\bar{x} \in W [/tex] is an equilibrium of the differential equation
(1) [tex]x' = f(x)[/tex]
where [tex]f : W \rightarrow E [/tex] is a [tex]C^1[/tex] map from an open set W of the vector space [tex]E[/tex] into [tex]E[/tex].
Then [tex]\bar{x}[/tex] is a stable equilibrium if for every neighborhood [tex]U[/tex] of [tex]\bar{x}[/tex] in [tex]W[/tex] there is a neighborhood [tex]U_1[/tex] of [tex]\bar{x}[/tex] in [tex]U[/tex] such that every solution [tex]x(t)[/tex] with [tex]x(0)[/tex] in [tex]U_1[/tex] is defined and in [tex]U[/tex] for all [tex] t > 0[/tex]. (See Fig. A.)
Fig A:
http://i50.photobucket.com/albums/f348/XavvaX/Smale1.png?t=1274719313
Should it be U instead of U_1 in the definition and vice versa? I say this because x(t) is not defined in U for all t > 0, but rather, defined in U_1. However, I don't know if I'm just misreading the definition and/or the picture. However, in the other picture describing asymptotic stability, they also use the same notation.
Fig B:
http://i50.photobucket.com/albums/f348/XavvaX/Smale2.png?t=1274720012
Definition 1: Suppose [tex]\bar{x} \in W [/tex] is an equilibrium of the differential equation
(1) [tex]x' = f(x)[/tex]
where [tex]f : W \rightarrow E [/tex] is a [tex]C^1[/tex] map from an open set W of the vector space [tex]E[/tex] into [tex]E[/tex].
Then [tex]\bar{x}[/tex] is a stable equilibrium if for every neighborhood [tex]U[/tex] of [tex]\bar{x}[/tex] in [tex]W[/tex] there is a neighborhood [tex]U_1[/tex] of [tex]\bar{x}[/tex] in [tex]U[/tex] such that every solution [tex]x(t)[/tex] with [tex]x(0)[/tex] in [tex]U_1[/tex] is defined and in [tex]U[/tex] for all [tex] t > 0[/tex]. (See Fig. A.)
Fig A:
http://i50.photobucket.com/albums/f348/XavvaX/Smale1.png?t=1274719313
Should it be U instead of U_1 in the definition and vice versa? I say this because x(t) is not defined in U for all t > 0, but rather, defined in U_1. However, I don't know if I'm just misreading the definition and/or the picture. However, in the other picture describing asymptotic stability, they also use the same notation.
Fig B:
http://i50.photobucket.com/albums/f348/XavvaX/Smale2.png?t=1274720012