We present conditions for the origin to be a centre for a class of cubic systems. Some of the centre conditions are determined by finding complicated invariant functions. We also investigate the coexistence of fine foci and the simultaneous bifurcation of limit cycles from them.
|Rhif yr erthygl||119|
|Nifer y tudalennau||23|
|Cyfnodolyn||Electronic Journal of Differential Equations|
|Statws||Cyhoeddwyd - 2007|