Eleny-Nicoleta Ionel (born April 1969) is a Romanian mathematician whose research concerns symplectic geometry, including the study of the Gromov–Witten invariants and Gopakumar–Vafa invariants. Among her most significant results are the proofs of Gopakumar-Vafa conjectures (joint with Thomas H. Parker et. al.), and the proof of Getzler's conjecture, asserting vanishing in codimension at least g of the tautological ring of the moduli space of genus-g curves.
She is a professor of mathematics at Stanford University, where she was chair of the mathematics department from 2016 to 2019.
Ionel is from Iași. She is the daughter of Adrian Ionel, a professor at the Ion Ionescu de la Brad University of Agricultural Sciences and Veterinary Medicine of Iași. She attended the prestigious Costache Negruzzi National College, graduating in 1987. She earned a bachelor's degree from Alexandru Ioan Cuza University in 1991, and completed her Ph.D. in 1996 from Michigan State University. Her dissertation, Genus One Enumerative Invariants in
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After postdoctoral research at the Mathematical Sciences Research Institute in Berkeley, California and a position as C. L. E. Moore instructor at the Massachusetts Institute of Technology, she joined the University of Wisconsin–Madison faculty in 1998, and moved to Stanford in 2004.
Ionel is a Sloan Research Fellow and a Simons Fellow. She was an invited speaker at the International Congress of Mathematicians in 2002. She was selected as a Fellow of the American Mathematical Society in the 2020 Class, for "contributions to symplectic geometry and the geometric analysis approach to Gromov–Witten Theory".