Stephen J. Willson

Professor
Mathematics Department
Iowa State University
Ames, IA 50011

Office: 411 Carver

Telephone: (515)-294-7671

FAX: (515)-294-5454

Course webpages for Fall 2008

Course webpages for Spring 2009

Tentative office hours for Fall 2008:

MWF 2:10 - 3:00, and TTh 3:10 - 4:00 in 411 Carver.
Please also feel free to make an appointment if the office hours are inconvenient for you.

Education:

A.B., Mathematics, Harvard University (magna cum laude), 1968
M.A., Mathematics, University of Michigan (Ann Arbor), 1970
Ph.D., Mathematics, University of Michigan (Ann Arbor), 1973

Professional experience:

1973-77, Assistant Professor of Mathematics, Iowa State University
1977-82, Associate Professor of Mathematics, Iowa State University
1982-, Professor of Mathematics, Iowa State University
1992-95, Chair, Mathematics Department, Iowa State University

Research interests:

Computational biology, especially building phylogenetic trees and networks. Supertrees. Game theory and fair division problems. Cellular automata. Fractals and chaotic dynamics.

Links for talks

Information on computational biology:

For more information about my work on building phylogenetic trees, click trees

To get my software for building phylogenetic trees, click software

For more information about the Laurence H. Baker Center for Bioinformatics and Biological Statistics click CBBS

Software in game theory:

Selected publications:

Equivariant maps between representation spheres, Pacific J. Math 56 (1975): 291-296.
The converse to the Smith theorem for Zp-homology spheres, Pacific J. Math 56 (1975): 597-605.
On the ergodic theory of cellular automata, Math. Systems Theory 9 (1975): 132-141.
Equivariant homology theories on G-complexes, Trans. Amer. Math. Soc. 212 (1975): 155-171.
Homological dimensions of the isotropy ring, Duke Math. J. 43 (1976): 159-170.
The orbit space of a sphere by an action of Zps, Proc. Amer. Math. Soc. 59 (1976): 361-365.
The growth of configurations, Math. Systems Theory 10 (1977): 387-400.
Limiting shapes for configurations, J. Comput. System Sci. 15 (1977): 243-261.
On convergence of configurations, Discrete Math. 23 (1978): 279-300.
A semigroup on the space of compact convex bodies, SIAM J. Math. Anal. 11 (1980): 448-457.
Growth patterns of ordered cellular automata. J. Comput. System Sci. 22 (1981): 29-41.
Cellular automata can generate fractals, Discrete Applied Mathematics 8 (1984): 91-99.
Growth rates and fractional dimensions, Physica 10D (1984): 69-74.
On coherent growth of configurations, SIAM J. Math. Anal. 16 (1985): 316-330.
A use of cellular automata to obtain families of fractals, in M.F. Barnsley and S.G. Demko, eds., "Chaotic Dynamics and Fractals," Academic Press, Orlando, 1986, 123-140.
The equality of fractional dimensions for certain cellular automata, Physica 24D (1987): 179-189.
Computing fractal dimensions for additive cellular automata, Physica 24D (1987): 190-206.
Convergence of iterated median rules, Computer Vision, Graphics, and Image Processing 47 (1989): 105-110.
Decision procedures for openness and local injectivity, Complex Systems 5 (1991): 497-508.
Calculating growth rates and moments for additive cellular automata, Discrete Applied Mathematics 35 (1992): 47-65.
Iterating maps on cellular complexes, Trans. A.M.S. 332 (1992): 225-240.
A value for partially defined cooperative games, International Journal of Game Theory 21 (1993): 371-384.
Computing fair divisions with various formulations of fairness, preprint (1995).
Long-term behavior in the theory of moves, Theory and Decision 45 (1998): 201-240.
Measuring inconsistency in phylogenetic trees, Journal of Theoretical Biology 190 (1998) 15-36.
Evaluations of fractal geometry and invariant moments for shape classification of corn germplasm (with Suranjan Panigrahi and Manjit K. Misra), Computers and electronics in agriculture 20 (1998) 1-20.
Building phylogenetic trees from quartets by using local inconsistency measures, Molecular Biology and Evolution 16 (1999): 685-693.
A higher-order parsimony method to reduce long-branch attraction, Molecular Biology and Evolution 16 (1999): 694-705.
Axioms for the outcomes of negotiation in matrix games, Mathematical Social Sciences 39 (2000): 323-348.
An error correcting map for quartets can improve the signals for phylogenetic trees, Molecular Biology and Evolution 18 (2001): 344-351.
Money-egalitarian-equivalent and gain-maximin allocations of indivisible items with monetary compensation, Social Choice and Welfare 20 (2003): 247-259.
Constructing rooted supertrees using distances, Bulletin of Mathematical Biology 66 no 6 (2004): 1755-1783.
Dan Ashlock, Stephen Willson, and Nicole Leahy. Coevolution and Tartarus. Proceedings of CEC 2004 (Congress on Evolutionary Computation).
Dan Ashlock, Kenneth Bryden, Steven Corns, and Stephen Willson. An improved taxonomy of evolutionary computation problems. Conference proceedings for ANNIE 2004 (Artificial Neural Networks in Engineering).
Minimum evolution using ordinary least squares is less robust than neighbor-joining, Bulletin of Mathematical Biology 67 (2005) 261-279.
Kenneth M. Bryden, Daniel A. Ashlock, Steven Corns, and Stephen J. Willson. Graph Based Evolutionary Algorithms. IEEE Transactions on Evolutionary Computation 10 (2006) 550-567..
Consistent formulas for estimating the total lengths of trees. Discrete Applied Mathematics 148 (2005) 214-239.
Unique solvability of certain hybrid networks from their distances. Annals of Combinatorics 10 (2006) 165-178.
Unique reconstruction of tree-like phylogenetic networks from distances between leaves. Bulletin of Mathematical Biology 68 (2006) 919-944.
Unique determination of some homoplasies at hybridization events. Bulletin of Mathematical Biology 69 (2007) 1709-1725.
Reconstruction of some hybrid phylogenetic networks with homoplasies from distances. Bulletin of Mathematical Biology 69 (2007) 2561-2590.
Reconstruction of certain phylogenetic networks from the genomes at their leaves. Journal of Theoretical Biology 252 (2008) 338-349.
Robustness of topological supertree methods for reconciling dense incompatible data. To appear in IEEE/ACM Transactions on Computational Biology and Bioinformatics.
Properties of normal phylogenetic networks, preprint 2008.

Vita

Pdf copy of my C.V.

Personal information:

My wife is Lee Anne Willson , who is a University Professor at Iowa State University in the Department of Physics and Astronomy . Her research typically involves mechanisms and implications of mass loss from stars, with particular emphasis on variable stars. My daughter, Kendra Willson, has interests in linguistics, Scandinavian, and dragons. My son, Jeffrey Willson, with substantial interests in physics, mathematics, music, and literature, is a graduate student in the Department of Physics and Astronomy at Iowa State University.

My recreations and hobbies include:

playing piano, especially classical piano
singing (I have a baritone voice and sing in the Ames Choral Society)
listening to music
windsurfing and kayaking
bird-watching (See Big Bluestem Audubon Society )
cross-country skiing
hiking
bicycling

Here is how to find more information about the Mathematics Department at Iowa State University.

Last updated September 22, 2008.