[求助]mathematica作业：解微分方程（急）

[emmanuelle]

x' = a + x^2 y -(b+1)x + f cos(ωt)
y' = b x - x^2 y
Start with a = 0.4, b = 1.2, f=0.05 and ω=0.6, which should settle into a
nice cycle. Raise the ω values toward 1.0 at the necessary increments to
produce period doubling and eventual chaos.
题目里ms没有给initial condition
还请熟悉mathematica的大虾给指条明路。。。谢谢