Problem with Ode Solver

The differential equation is y''+ 5y'+7y=0, with y(0)=12 and y'(0)=21. Accordingly, I created a matlab function

function dxdt=odeprac(t,x)
dxdt =[x(2); -7*x(1)-5*x(2)];

Here, y=x(1) and y'=x(2) If I run the command

[t,x] = ode45(@odeprac,tspan,[21; 12]);
>> plot(t,x(1));

Then I do not get the time path of y (which, ideally, should show waves), but a horizontal line at x1=21. Even rescaling the axes or trying other ode solver do not help.

What other options I may try?

Answer 1

[Torsten]

1. The vector of Initial values is [12 21].

2. The plot command must read

   plot (t,x(:,1));

Best wishes

Torsten.