PLotting a graph of third order differential equation

syms y(x) 
eqn = 2*diff(y,x,3)+9*diff(y,x,2)+12*diff(y,x,1)+5*y == 0;
ySol = dsolve(eqn)
z = eval(vectorize(ySol));
plot(ySol,z)

[Torsten]

Before you can plot anything, you must specify three initial conditions.

Answer 1

[Star Strider]

The initial conditions are not provided, and it is not possible to plot a function with symbolic (or otherwise undefined) parameters.

Try this —

syms y(x) y0 Dy0 D2y0 
Dy = diff(y);
D2y = diff(Dy);
D3y = diff(D2y);
eqn = 2*diff(y,x,3)+9*diff(y,x,2)+12*diff(y,x,1)+5*y == 0;
ySol = dsolve(eqn, y(0)==y0, Dy(0)==Dy0, D2y(0)==D2y0) 

ySol = 

ySol = subs(ySol, {y0, Dy0, D2y0},{1,2,3})                      % Substitute (Or Initially Supply) Initial Conditions

ySol = 

figure
fplot(ySol, [0 10])
grid

.