We give some properties of the saddle conic of quadratic differential systems. We also deduce semi-algebraic conditions for the existence of one, two or three saddle points (in terms of affine invariants).
Submitted December 16, 1999. Published March 28, 2000.
Math Subject Classifications: 34C05, 34C20.
Key Words: nonlinear differential systems, saddle points, qualitative theory of ordinary differential systems, critical points, invariant theory.
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| Driss Boularas |
LACO, Departement de Mathematiques
Faculte des Sciences, Universite de Limoges
123, Avenue A. Thomas, 87060, Limoges, France
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