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Note on parametrisations of normal elliptic scrolls

Published online by Cambridge University Press:  26 February 2010

P. Du Val
Affiliation:
Mathematics Department, University College London, Gower Street, W.C.1.
J. G. Semple
Affiliation:
Mathematics Department, King's College London, Strand, W.C.2.
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1. If w(mod 2ω1, 2ω2) is an elliptic parameter for points of a normal elliptic curve C = 1Cn[n − 1], then it is well known that the sets of n points in which C is met by primes have a constant parameter sum k (mod 2ωl, 2ω2), and we may express this for convenience by saying that k is the prime parameter sum for the parametrisation of C by w. If we take the origin of w (the point for which w ≡ 0) to be one of the points of hyperosculation of C, then k ≡ 0, and we may say that w is a normal parameter for C. In the same way, if Γ is the Grassmannian image curve of the generators of a normal elliptic scroll 1R2n[n − 1], then a normal parametrisation of Γ defines a normal parameter w for the generators of 1R2n, such that n of the generators have parameter sum zero if and only if they belong to a linear line-complex not containing all the generators of 1R2n; or, in particular, if they all meet a space [n – 3] that is not met by every generator of the scroll. In this paper we are concerned in the first instance with the type of normal elliptic scroll 1R22m+1[2m] whose points can be represented by the unordered pairs (u1; u2) of values of an elliptic parameter u(mod 2ω1, 2ω2); and we establish a significant connection between any normal parametrisation of the generators of 1R2m+1 and an associated parametric representation (u1u2) of its points. We also add a brief note to indicate the lines along which this kind of connection can be extended to apply to a general normal elliptic scrollar variety 1Rkmk+1[mk] whose points can be represented by the unordered sets (u1, …, uk) of values of an elliptic parameter u.

Type
Research Article
Copyright
Copyright © University College London 1970

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References

1.Segre, C., “Remarques sur les transformations uniformes des courbes elliptiques en elles-meme”, Opere Vol. I, 3655 (Rome, 1957).Google Scholar
2.Segre, C., “Ricerche sulle rigate ellittiche di qualunque ordine”, Opere, Vol. I, 5677 (Rome, 1957).Google Scholar
3.Semple, J. G. and Tyrrell, J. A., “The Cremona transformation of S 6 by quadrics through a normal elliptic septimic scroll 1R 7”, Mathematika 16 (1969), 8897.CrossRefGoogle Scholar