Rodica Simion

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. She graduated from the University of Bucharest in 1974, and immigrated to the United States in 1976. She did her graduate studies at the University of Pennsylvania, earning a Ph.D. in 1981 under the supervision of Herbert Wilf. 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.

Simion's thesis research concerned the concavity and unimodality of certain combinatorially defined sequences, and included what Richard P. Stanley calls "a very influential result" that the zeros of certain polynomials are all real.

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. The "simsun permutations" were named after her and Sheila Sundaram, after their initial studies of these objects; 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.

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