Nonzero periodic solutions of nonautonomous systems of ordinary differential equations (Q1398493)

The author considers the bifurcation of forced periodic oscillations from the zero stationary solution of nonautonomous planar systems depending on a four-dimensional parameter vector. He suggests sufficient conditions for a parameter value to be a local bifurcation point in terms of entries of the matrix of the linearized system and the monodromy matrix of an equivalent linear system. An explanation of why a multidimensional parameter is considered is not presented.