Generic Initial ideals of Singular Curves in Graded Lexicographic Order

In this paper, we are interested in the generic initial ideals of \textit{singular} projective curves with respect to the graded lexicographic order. Let $C$ be a \textit{singular} irreducible projective curve of degree $d\geq 5$ with the arithmetic genus $ρ_a(C)$ in $\p^r$ where $r\ge 3$. If $M(I_C)$ is the regularity of the lexicographic generic initial ideal of $I_C$ in a polynomial ring $k[x_0,..., x_r]$ then we prove that $M(I_C)$ is $1+\binom{d-1}{2}-ρ_a(C)$ which is obtained from the monomial $x_{r-3} x_{r-1}\,^{\binom{d-1}{2}-ρ_a(C)},$ provided that $\dim\Tan_p(C)=2$ for every singular point $p \in C$. This number is equal to one plus the number of non-isomorphic points under a generic projection of $C$ into $\p^2$. %if $°(C)=3,4$ then $M(I_C)= °(C)$ by the direct computation. Our result generalizes the work of J. Ahn for \textit{smooth} projective curves and that of A. Conca and J. Sidman \cite{CS} for \textit{smooth} complete intersection curves in $\p^3$. The case of singular curves was motivated by \cite[Example 4.3]{CS} due to A. Conca and J. Sidman. We also provide some illuminating examples of our results via calculations done with {\it Macaulay 2} and \texttt {Singular} \cite{DGPS, GS}.

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