How do you plot nonlinear differential equations?

2013 4 15
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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?

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Peter
Peter 2013-4-16
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
Yao Li 2013-4-16
Do Dx and Dy equal to dx/dt and dy/dt or just dx and dy?

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Peter
Peter
2013-4-15

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