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How do you plot nonlinear differential equations?

Asked by Peter on 15 Apr 2013

Dx=y

Dy=-k*y-x^3+9.8*cos(t)

inits=('x(0)=0,y(0)=0')

these are the differential equations that I wanted to plot.

first, I tried to solve the differential equation and then plot the graph.

Dsolve('Dx=y','Dy=-k*y-x^3+9.8*cos(t)', inits)

like this, however, there matlab is telling me that it has no explicit solution for this system.

now i am stuck :(

how can you plot this system without solving the equations?

2 Comments

Peter on 16 Apr 2013

by others help,

k = 1;

f = @(t,x) [x(2); -k * x(2) - x(1)^3 + 9.8 * cos(t)];

tspan = [0, 10];

xinit = [0, 0];

ode45(f, tspan, xinit)

If I do this I get a graph of x(1)vs t/x(2)vs t seperately, however the graph I wanted was x(2)vs x(1).

Can anyone help me with this?

Yao Li on 16 Apr 2013

Do Dx and Dy equal to dx/dt and dy/dt or just dx and dy?

Peter

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