Example 3.  Solve the second order  I.V.P.  
    [Graphics:Images/PendulumMod_gr_60.gif]  with  [Graphics:Images/PendulumMod_gr_61.gif],   [Graphics:Images/PendulumMod_gr_62.gif].    

Solution 3.

The D. E. can be written as   [Graphics:../Images/PendulumMod_gr_63.gif]  where  [Graphics:../Images/PendulumMod_gr_64.gif].  
We use the substitution [Graphics:../Images/PendulumMod_gr_65.gif]  and make the second order I.V.P. into a system of first order I.V.P.'s  

    [Graphics:../Images/PendulumMod_gr_66.gif],  
and  
    [Graphics:../Images/PendulumMod_gr_67.gif],  
where  
    [Graphics:../Images/PendulumMod_gr_68.gif],  
and  
     [Graphics:../Images/PendulumMod_gr_69.gif],   [Graphics:../Images/PendulumMod_gr_70.gif].  

 

 

[Graphics:../Images/PendulumMod_gr_71.gif]



[Graphics:../Images/PendulumMod_gr_72.gif]
[Graphics:../Images/PendulumMod_gr_73.gif]
[Graphics:../Images/PendulumMod_gr_74.gif]
[Graphics:../Images/PendulumMod_gr_75.gif]

Compute the Runge-Kutta solution.

[Graphics:../Images/PendulumMod_gr_76.gif]

The solution we seek is the first coordinate in the 2D system.

[Graphics:../Images/PendulumMod_gr_77.gif]

Now we can plot the solution.

[Graphics:../Images/PendulumMod_gr_78.gif]


[Graphics:../Images/PendulumMod_gr_79.gif]

[Graphics:../Images/PendulumMod_gr_80.gif]
[Graphics:../Images/PendulumMod_gr_81.gif]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(c) John H. Mathews 2004