y-nullclines
The -nullclines are found by setting the RHS of the second ODE equal to 0:
> factor( rhs(ode2) ) = 0 ;
The -nullcline(s) typically consists of curves that can be expressed either as a function of or as a function of :
> yNULL1 := plot( 0, x = -1 .. 10, color=BLUE ): # for a nullcline of the form y=F(x)
> yNULL2 := plot( [ 4, y, y = -5 .. 5 ], color=BLUE ): # for a nullcline of the form x=G(y)
> yNULLplot := display( [ yNULL1, yNULL2 ], axes=BOXED ):
> yNULLplot;
>