thank you very much!

It helped me a lot.

again a  question for the constraint:

I tried to do a plot of phase plane with phase portrait but  it doesn't work if I had the constraint with :  Heaviside(x(N)^2+y(N)^2-1)*I

do you know how I can do that?

phaseportrait([diff(x(N),N)=-3*x(N)+sqrt(6)*(y(N))^2+3/2*x(N)*((x(N))^2+1-(y(N))^2),diff(y(N),N)=-sqrt(6)*x(N)*y(N)+3/2*y(N)*((x(N))^2+1-(y(N))^2)],[x(N),y(N)],N=0..200,[[x(0)=-0.99,y(0)=0.01],[x(0)=0,y(0)=0.01],[x(0)=0.99,y(0)=0.1],[x(0)=-0.9,y(0)=0.2],[x(0)=-0.5,y(0)=0.01],[x(0)=0.96,y(0)=0.25]],stepsize=.05,linecolor=[gold,yellow,red,green,blue,wheat]);

thank you very much!

It helped me a lot.

again a  question for the constraint:

I tried to do a plot of phase plane with phase portrait but  it doesn't work if I had the constraint with :  Heaviside(x(N)^2+y(N)^2-1)*I

do you know how I can do that?

phaseportrait([diff(x(N),N)=-3*x(N)+sqrt(6)*(y(N))^2+3/2*x(N)*((x(N))^2+1-(y(N))^2),diff(y(N),N)=-sqrt(6)*x(N)*y(N)+3/2*y(N)*((x(N))^2+1-(y(N))^2)],[x(N),y(N)],N=0..200,[[x(0)=-0.99,y(0)=0.01],[x(0)=0,y(0)=0.01],[x(0)=0.99,y(0)=0.1],[x(0)=-0.9,y(0)=0.2],[x(0)=-0.5,y(0)=0.01],[x(0)=0.96,y(0)=0.25]],stepsize=.05,linecolor=[gold,yellow,red,green,blue,wheat]);