### Abstract

Original language | English |
---|---|

Pages (from-to) | 547-552 |

Journal | Bulletin of the London Mathematical Society |

Volume | 22 |

Issue number | 6 |

DOIs | |

Publication status | Published - 1990 |

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*Bulletin of the London Mathematical Society*,

*22*(6), 547-552. https://doi.org/10.1112/blms/22.6.547

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*Bulletin of the London Mathematical Society*, vol. 22, no. 6, pp. 547-552. https://doi.org/10.1112/blms/22.6.547

**Euler Characteristics of Real Varieties.** / Bruce, J.W.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Euler Characteristics of Real Varieties

AU - Bruce, J.W.

PY - 1990

Y1 - 1990

N2 - In this paper we show how to associate to any real projective algebraic variety Z ⊂ RPn−1 a real polynomial F1:Rn,0 → R, 0 with an algebraically isolated singularity, having the property that χ(Z) = ½(1 − deg (grad F1), where deg (grad F1 is the local real degree of the gradient grad F1:Rn, 0 → Rn, 0. This degree can be computed algebraically by the method of Eisenbud and Levine, and Khimshiashvili [5]. The variety Z need not be smooth. This leads to an expression for the Euler characteristic of any compact algebraic subset of Rn, and the link of a quasihomogeneous mapping f: Rn, 0 → Rn, 0 again in terms of the local degree of a gradient with algebraically isolated singularity. Similar expressions for the Euler characteristic of an arbitrary algebraic subset of Rn and the link of any polynomial map are given in terms of the degrees of algebraically finite gradient maps. These maps do involve ‘sufficiently small’ constants, but the degrees involved ar (theoretically, at least) algebraically computable.

AB - In this paper we show how to associate to any real projective algebraic variety Z ⊂ RPn−1 a real polynomial F1:Rn,0 → R, 0 with an algebraically isolated singularity, having the property that χ(Z) = ½(1 − deg (grad F1), where deg (grad F1 is the local real degree of the gradient grad F1:Rn, 0 → Rn, 0. This degree can be computed algebraically by the method of Eisenbud and Levine, and Khimshiashvili [5]. The variety Z need not be smooth. This leads to an expression for the Euler characteristic of any compact algebraic subset of Rn, and the link of a quasihomogeneous mapping f: Rn, 0 → Rn, 0 again in terms of the local degree of a gradient with algebraically isolated singularity. Similar expressions for the Euler characteristic of an arbitrary algebraic subset of Rn and the link of any polynomial map are given in terms of the degrees of algebraically finite gradient maps. These maps do involve ‘sufficiently small’ constants, but the degrees involved ar (theoretically, at least) algebraically computable.

U2 - 10.1112/blms/22.6.547

DO - 10.1112/blms/22.6.547

M3 - Article

VL - 22

SP - 547

EP - 552

JO - Bulletin of the London Mathematical Society

JF - Bulletin of the London Mathematical Society

SN - 0024-6093

IS - 6

ER -