Topological Lower Bounds on the Number of Real Solutions

Frank Sottile
University of Massachusetts-Amherst
Invited Talk, Solving Systems of Polynomial Equations,

It is a difficult problem to say anything meaningful about the number of real solutions to a system of equations. Recently, Eremenko and Gabrielov introduced a notion, that of the real degree of a projection map, that can give a non-trivial lower bound on the number of real solutions to some systems of polynomial equations.

In this talk, I will describe this idea of Eremenko and Gabrielov, give some applications, and discuss its limitations. In addition, I will show how this degree may be computed for some projections of some toric varieties.