Mathematics Department

Iowa State University

Ames, IA 50011

Office: Carver 411

Telephone: (515)-294-7671

FAX: (515)-294-5454

E-mail: swillson@iastate.edu

- 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

- 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
- 2009-12, Janson Professor of Mathematics, Iowa State University
- 2010-, University Professor, Iowa State University

- Mathematical organizations
- Restrictions on meaningful phylogenetic networks
- Reconstructing regular networks from their trees 4
- Overview of Bioinformatics and Computational Biology Undergraduate Major (BCBio)
- ISU Services
- Tree-AverageDis2

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

- Source Code in Pascal for Theory of Moves
- Executable Code for Theory of Moves designed for Power Macintosh

- 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. IEEE/ACM Transactions on Computational Biology and Bioinformatics 6 (2009) 62-75.
- Properties of normal phylogenetic networks, Bulletin of Mathematical Biology 72 (2010) 340-358.
- Regular networks are determined by their trees, IEEE/ACM Transactions on Computational Biology and Bioinformatics 8 (2011) 785-796.
- Restricted trees: simplifying networks with bottlenecks, Bulletin of Mathematical Biology (2011) 73, 2322-2338.
- CSD Homomorphisms Between Phylogenetic Networks.
*IEEE/ACM Transactions on Computational Biology and Bioinformatics*(2012) 9: 1128-1138. - Tree-average distances on certain phylogenetic networks have their weights uniquely determined.
*Algorithms for Molecular Biology*(2012) 7:13, doi:10.1186/1748-7188-7-13. - Reconstruction of certain phylogenetic networks from their tree-average distances.
*Bulletin of Mathematical Biology.*(2013) 75(10), 1840-1878. - Comparing and simplifying distinct-cluster phylogenetic networks. Submitted.

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

Last updated January 13, 2015.