Titre : Comptes rendus de l'Académie des sciences. Série 1, Mathématique
Auteur : Académie des sciences (France). Auteur du texte
Éditeur : Elsevier (Paris)
Éditeur : Centrale des revuesCentrale des revues (Montrouge)
Éditeur : ElsevierElsevier (Paris)
Date d'édition : 1987-09-30
Notice du catalogue : http://catalogue.bnf.fr/ark:/12148/cb34394200t
Type : texte texte
Type : publication en série imprimée publication en série imprimée
Langue : français
Format : Nombre total de vues : 29122 Nombre total de vues : 29122
Description : 30 septembre 1987 30 septembre 1987
Description : 1987/09/30 (SER1,T305,N10). 1987/09/30 (SER1,T305,N10).
Droits : Consultable en ligne
Identifiant : ark:/12148/bpt6k5494281t
Source : Archives de l'Académie des sciences, 2008-94315
Conservation numérique : Bibliothèque nationale de France
Date de mise en ligne : 01/12/2010
- Aller à la page de la table des matièresI
- CONTENTS 1987 - VOLUME 305 - SECTION I - N° 10
- .......... Page(s) .......... 393
- .......... Page(s) .......... 393
- A new proof of existence for "strong Frobenius structure" of the hypergeometric differential equation is given. The interest of this proof lies in the fact that the geometric interpretation of the equation as "Picard-Fuchs equation" is not used.
- .......... Page(s) .......... 397
- It is shown that the set of squares
and, more generally, a set of the form
where p(n) is any polynomial taking integer values, satisfies the pointwise ergodic theorem for L2-functions. This gives an affirmative answer to a problem considered by A. Bellow and H. Furstenberg. The previous result generalizes to commuting systems of transformations.
- .......... Page(s) .......... 403
- .......... Page(s) .......... 403
- The aim of this Note is to show by an explicit verification, that the stable category of a self injective finite dimensional algebra over a field, graded by the inverse of the equivalence induced by the Heller operator, is triangulated (cf. [2]).
- .......... Page(s) .......... 407
- To every homogeneous polynomial P on Rk we associate a triplet of differential operators (X_, X0, X+) on the same space, which satisfies the commutation relations of the usual basis of sl (2, R) and such that X+ = Cte P(x). We examine more closely the case where P is the relative invariant of a prehomogeneous vector space and give, in some cases, the decomposition of the space of regular functions on the open orbit.
- .......... Page(s) .......... 411
- We consider the uniqueness of the inverse scattering problem for the wave equation . If and if the asymptotic wave profiles related to coincide for , then .
- .......... Page(s) .......... 415
- We study the Klein-Gordon symbolic calculus of operators acting on solutions of the free Klein-Gordon equation. It contracts to the Weyl calculus as . Mathematically, it may also be considered as a pseudodifferential analysis on the unit ball of Rn.
- .......... Page(s) .......... 419
- .......... Page(s) .......... 419
- Let E be a holomorphic vector bundle of rank r over a compact complex manifold X of dimension n. If E is positive in the sense of Griffiths, it is shown that the Dolbeault cohomology groups vanish for and . The proof rests on the well-known fact that any tensor power splits into irreductible representations of Gl(E), each component being canonically isomorphic to the space of sections of a positive homogeneous line bundle over a flag manifold of E. The vanishing property is then obtained by a combination of Le Potier's isomorphism theorem with a new curvature estimate for the bundle of X-relative differential forms on the flag manifold of E.
- .......... Page(s) .......... 431
- .......... Page(s) .......... 431
- We propose a particle method of resolution of convection-diffusion equations which is a generalization of the one proposed in [1]. The method is based on the approximation of a diffusion operator by an integral operator and consists in two steps: the approximation of the solution of the convection-diffusion problem by the solution of the obtained integro-differential equation and the resolution of the integro-differential equation by a particle method.
- All rational curves are determined with Bernstein polynomials by a polygon of control weighted points and control vectors. Stable algorithms for computing any point are given with a view to their applications in CAD. CAM and robotics.
- .......... Page(s) .......... 441
- .......... Page(s) .......... 441
- We determine, by homogenization, the limit load of a periodic nonhomogeneous structure. For a structure clamped on its boundary it was proposed [1] and proved [4] that the problem reduces to a limit load problem for an homogenized structure the strength capacity of which was characterized. For a structure loaded on its boundary the present work shows that the limit load problem must include an additional strength criterion on the stress vector on the boundary. This strength criterion is more restrictive than the condition which can be deduced from the bulk strength capacity.
- COMPTES RENDUS DE L'ACADEMIE DES SCIENCES
- MATHEMATIQUE 1987 - Tome 305 - Série I - n° 10
- Théorie des nombres
- Algèbre
- .......... Page(s) .......... 403
- Théorie des groupes
- .......... Page(s) .......... 407
- Analyse mathématique
- .......... Page(s) .......... 415
- Analyse complexe
- Analyse fonctionnelle
- .......... Page(s) .......... 423
- Géométrie différentielle
- .......... Page(s) .......... 427
- Analyse numérique
- .......... Page(s) .......... 431
- Problèmes mathématiques de la mécanique
- .......... Page(s) .......... 441
C. R. Acad, Sci. Paris, t. 305, Série I, p. 435-440, 1987 435
Analyse numérique/iVM?nericaZ Analysis
Nouvelle description et calcul des courbes rationnelles à
l'aide de points et de vecteurs de contrôle
Jean-Charles FIOROT et Pierre JEANNIN
Résumé — Toutes les courbes rationnelles sont déterminées à l'aide des polynômes de Bernstein
par un polygone de points pondérés et de vecteurs de contrôle. Des algorithmes stables de calcul
sur ordinateur de tout point sont donnés en vue de leur application en CAO, CFAO et robotique.
New description and computation of rational curves with control points and control
vectors
Abstract — AU rational curves are determined with Bernstein polynomials by a polygon of control
weighted points and control vectors. Stable algorithms for Computing any point are given with a view
to their applications in CAD, CAM and robotics.
AbridgedEnglish version —- Let us define S (resp. J*) a real affine space, S (resp. J5") its asso-
ciated linear vector space such that S (resp. S) is an hyperplan of #" (resp. of J5") and S the real
projective space associated to S. Let us consider a point Q in J^ not belonging to S and the
following linear vector space l=(#xR*)U^ [i]- Let us define Ô : S -> 3F by
Û(M, a)=aftM, Q(u)=u.
We dénote by "©" and "*" (resp. "+" and ".") die addition operator and the external
multiplication operator in S (resp. eJ5"). For 8 and 0'e -9©e' = â-1(Ô(e)+Q(e')), X*Q=Ù-1(X.Û(e)). We prove that Û is an isomorphism
from (tre to weighted points and vectors and gives a géométrie construction with a straightedge and a
compass of an affine linear corrfbination of two points of S.
We dénote by D.1 an origin of §\ ai rational curve [(RC) in abrev] is given by
fiIM(t) = (S(f))~ 1 W(t), te[0, 1] where W(t) is a polynomiai, the coefficients of which are
vectors ofdefined by continuity.
Let us give the following définition [7] of (RC) of S : 0O, 0l5 ... 0„ are (n +1) points of S, I
and I with IUÏ={0, 1, . . ., n}, lf\l=0 such that : G—fP,-, P,-)e ieï; a rational Bézier curve of degree n, associated to the polygon (0O, 01; . . ., 0„) is the curve
defined by P(t) e I for t e [0, 1] where :
P(t) = (v(t))00, the point at infmity in the direction
and v(t) #0; in the other cases we define P (t) by continuity.
The points P; and the scalars~p\- are called control points and control weights respectively, the
vectors U,-, control vectors. We prove that any (RC) can be written in the form (1) and (2).
In the littérature, classical (RC) are described by positive weighted points ([6], [3], [11]), for
degree « = 2, 3 see [9], [4]. Recèntly in [12] the author introduces the notion of infinité control
points.
Note présentée par Jacques-Louis LIONS.
0249-6291/87/03050435 $ 2.00 © Académie des Sciences
Analyse numérique/iVM?nericaZ Analysis
Nouvelle description et calcul des courbes rationnelles à
l'aide de points et de vecteurs de contrôle
Jean-Charles FIOROT et Pierre JEANNIN
Résumé — Toutes les courbes rationnelles sont déterminées à l'aide des polynômes de Bernstein
par un polygone de points pondérés et de vecteurs de contrôle. Des algorithmes stables de calcul
sur ordinateur de tout point sont donnés en vue de leur application en CAO, CFAO et robotique.
New description and computation of rational curves with control points and control
vectors
Abstract — AU rational curves are determined with Bernstein polynomials by a polygon of control
weighted points and control vectors. Stable algorithms for Computing any point are given with a view
to their applications in CAD, CAM and robotics.
AbridgedEnglish version —- Let us define S (resp. J*) a real affine space, S (resp. J5") its asso-
ciated linear vector space such that S (resp. S) is an hyperplan of #" (resp. of J5") and S the real
projective space associated to S. Let us consider a point Q in J^ not belonging to S and the
following linear vector space l=(#xR*)U^ [i]- Let us define Ô : S -> 3F by
Û(M, a)=aftM, Q(u)=u.
We dénote by "©" and "*" (resp. "+" and ".") die addition operator and the external
multiplication operator in S (resp. eJ5"). For 8 and 0'e
from (
compass of an affine linear corrfbination of two points of S.
We dénote by D.1 an origin of §\ ai rational curve [(RC) in abrev] is given by
fiIM(t) = (S(f))~ 1 W(t), te[0, 1] where W(t) is a polynomiai, the coefficients of which are
vectors of
Let us give the following définition [7] of (RC) of S : 0O, 0l5 ... 0„ are (n +1) points of S, I
and I with IUÏ={0, 1, . . ., n}, lf\l=0 such that : G—fP,-, P,-)e
defined by P(t) e I for t e [0, 1] where :
P(t) = (v(t))00, the point at infmity in the direction
and v(t) #0; in the other cases we define P (t) by continuity.
The points P; and the scalars~p\- are called control points and control weights respectively, the
vectors U,-, control vectors. We prove that any (RC) can be written in the form (1) and (2).
In the littérature, classical (RC) are described by positive weighted points ([6], [3], [11]), for
degree « = 2, 3 see [9], [4]. Recèntly in [12] the author introduces the notion of infinité control
points.
Note présentée par Jacques-Louis LIONS.
0249-6291/87/03050435 $ 2.00 © Académie des Sciences
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