Defining the model

All differential equation models begin with a differential equation. If the problem is an intial value problem, an initial condition is also needed. Replace the question marks ( ? ) in the following input regions to define the relevant ODE model.

> ode1 := diff( x(t), t ) = y(t) * ( x(t)^2 + y(t)^2 - 1 ) :

> ode2 := diff( y(t), t ) = -x(t) * ( x(t)^2 + y(t)^2 - 1 ) :

> MODEL := { ode1, ode2 } ; # define the differential equation model

> IC := [ x(0) = 0, y(0) = 1/2 ] ; # specify an initial condition

> VAR := { x(t), y(t) } ; # identify the variables in the model

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