These exact solutions for the periodic travelling wave families enable a great deal of further analytical study. Exact conditions for the stability of the periodic travelling waves can be found,[1][2] and the condition for absolute stability can be reduced to the solution of a simple polynomial.[15][16] Also exact solutions have been obtained for the selection problem for waves generated by invasions[22][33] and by zero Dirichlet boundary conditions.[34][35] In the latter case, for the complex Ginzburg-Landau equation, the overall solution is a stationary Nozaki-Bekki hole.[34][36]