Complete intersections in certain affine and projective monomial curves (1407.7007v1)

Abstract: Let $k$ be an arbitrary field, the purpose of this work is to provide families of positive integers $\mathcal{A} = {d_1,\ldots,d_n}$ such that either the toric ideal $I_{\mathcal A}$ of the affine monomial curve $\mathcal C = {(t^{d_1},\ldots,\,t^{d_n}) \ | \ t \in k} \subset \mathbb{A}k^n$ or the toric ideal $I{\mathcal A^{\star}}$ of its projective closure ${\mathcal C^{\star}} \subset \mathbb{P}k^n$ is a complete intersection. More precisely, we characterize the complete intersection property for $I{\mathcal A}$ and for $I_{\mathcal A^{\star}}$ when: (a) $\mathcal{A}$ is a generalized arithmetic sequence, (b) $\mathcal{A} \setminus {d_n}$ is a generalized arithmetic sequence and $d_n \in \mathbb{Z}^+$, (c) $\mathcal{A}$ consists of certain terms of the $(p,q)$-Fibonacci sequence, and (d) $\mathcal{A}$ consists of certain terms of the $(p,q)$-Lucas sequence. The results in this paper arise as consequences of those in Bermejo et al. [J. Symb. Comput. 42 (2007)], Bermejo and Garc\'{\i}a-Marco [J. Symb. Comput. (2014), to appear] and some new results regarding the toric ideal of the curve.