Rodica Eugenia Simion (January 18, 1955 – January 7, 2000) was a Romanian-American mathematician. She was the Columbian School Professor of Mathematics at George Washington University. Her research concerned combinatorics: she was a pioneer in the study of permutation patterns, and an expert on noncrossing partitions.
Simion was one of the top competitors in the Romanian national mathematical olympiads.[1] She graduated from the University of Bucharest in 1974, and immigrated to the United States in 1976.[2] She did her graduate studies at the University of Pennsylvania, earning a Ph.D. in 1981 under the supervision of Herbert Wilf.[2][3] After teaching at Southern Illinois University and Bryn Mawr College, she moved to George Washington University in 1987, and became Columbian School Professor in 1997.[2]
She is included in a deck of playing cards featuring notable women mathematicians published by the Association of Women in Mathematics.[4]
Simion's thesis research concerned the concavity and unimodality of certain combinatorially defined sequences,[5] and included what Richard P. Stanley calls "a very influential result" that the zeros of certain polynomials are all real.[2]
Next, with Frank Schmidt, she was one of the first to study the combinatorics of sets of permutations defined by forbidden patterns; she found a bijective proof that the stack-sortable permutations and the permutations formed by interleaving two monotonic sequences are equinumerous, and found combinatorial enumerations of many permutation classes.[2][5] The "simsun permutations" were named after her and Sheila Sundaram, after their initial studies of these objects;[6][7] a simsun permutation is a permutation in which, for all k, the subsequence of the smallest k elements has no three consecutive elements in decreasing order.[8]
Simion also did extensive research on noncrossing partitions, and became "perhaps the world's leading authority" on them.[2]
Simion was the main organizer of an exhibit about mathematics, Beyond Numbers, at the Maryland Science Center, based in part on her earlier experience organizing a similar exhibit at George Washington University.[2][9] She was also a leader in George Washington University's annual Summer Program for Women in Mathematics.[2] As well as being a mathematician, Simion was a poet and painter;[6][10] her poem "Immigrant Complex" was published in a collection of mathematical poetry in 1979.[11]
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