Duffing oscillator with PyCont( use HB)

[aipozi]

Hi,Rob,I'm a studen und now i try to use Pydstool to solve Duffing oscillator and want to get the Amplitude-Frequency diagramm.
But now there is a question. Why is the part from the starting point to LP1 unstable? This part is stable through my mathematical calculations, but in this figure, only the stability of this part is different from the actual situation, and the other period All correct
Thanks!

from PyDSTool import *

gamma1=-1
D= 0.05
w_dach = 0.05
eta=0

Cstr='(1-etaeta)C+2DetaS+(3/4)gamma1(C**3+CS2)-w_dach'
Sstr='(1-etaeta)S-2Deta*C+(3/4)gamma1(S3+C2*S)'
qstr='sqrt(C2+S**2)-q'
PCargs = args(name='duff_cont', type='EP-C')
PCargs.freepars = ['eta']
PCargs.StepSize = 1e-3
PCargs.MaxNumPoints = 10000
PCargs.MaxStepSize = 1e-2
PCargs.LocBifPoints = ['LP', 'BP', 'B']
PCargs.StopAtPoints = ['B']
PCargs.verbosity = 2
PCargs.SaveEigen = True
PCargs.SaveJacobian = True
#PCargs.Corrector = 'MoorePenrose'

DSargs = args(name='duffing')
DSargs.pdomain = {'eta': [0, 1.6]} # domain boundaries
DSargs.varspecs = {'C': Cstr, 'S': Sstr,'q':qstr}
DSargs.ics = {'C': 0, 'S': 0,'q':0}
DSargs.pars = {'eta':eta,'gamma1': gamma1, 'D': D, 'w_dach': w_dach}
testDS = Generator.Vode_ODEsystem(DSargs)
PyCont = ContClass(testDS)
PyCont.newCurve(PCargs)
PyCont['duff_cont'].forward()
#PyCont.display(('eta', 'C'), stability=True)
#PyCont.display(('eta', 'S'), stability=True)
PyCont.display(('eta', 'q'), stability=True)