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Asked by Mike Randy
on 9 Sep 2013

first time using matlab, how can i use solve to find the equilibrium solutions of the differential equation, y` = -( 3 - y ) y

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Answer by the cyclist
on 9 Sep 2013

I would not use solve(). I would try ode45() to start.

doc ode45

for details and examples.

Answer by Roger Stafford
on 9 Sep 2013

Why bother using matlab when elementary differential equations techniques will easily give the solution:

y = 3/(1+k*exp(3*x))

for arbitrary constant k and with x the independent variable.

Youssef KHMOU
on 10 Sep 2013

Roger, can you add some details about how you obtained the solution ( explaining the variables separation ) because i think it is :

y=3/(1-k*exp(3*x))

Roger Stafford
on 10 Sep 2013

The two forms are entirely equivalent. Your k is the negative of my k. k can be either positive or negative depending on initial conditions.

Answer by Youssef KHMOU
on 10 Sep 2013

Like @the cylist said, try ode23 or ode45, but you did not mention the initial condition :

function dy=Myfunction(t,y) dy(1)=-(3-y(1)).*y(1);

In the workspace ( initial condition k=0.01 with time [0,,,,10]) :

>>[t,y]=ode45('Myfunction',0,10,0.010); >>plot(t,y)

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