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Runge Kutta-2
  Suppose we have ODE
  
   then
  
 
  
   Formula
  
  :
  
 
Where
  
   and
   
  
 
Other variation name : Improve Euler method, Heun's method, Midpoint method
  
   Error term
  
  :
  
   , correct up to the second order term in Taylor series expansion.
  
 
  The Taylor series expansion is
  
 
  The computation is using
  
   spreadsheet that can be downloaded here
  
  
  
   
  
 
Example:
  
   , set
   
    , with initial condition
    
     . The few first results and the graph of solution are given below.
    
   
  
 
  
 
  
 
  Note that after
  
   , the solution is not correct. See Comparison.
  
 
  Expanding the
  
   order Runge-Kutta formula, we have
  
 
  
 
  Second term of the right hand side [
  
   ] is the estimated range difference. The estimated range difference is computed based on a half of the slope at the
   
    beginning
   
   of the interval
   
    and the slope in the
    
     middle
    
    of the interval
    
     , as illustrated in the figure below
    
   
  
 
  
 
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  See also:
  
   Numerical Excel tutorial
  
  ,
  
   Dynamical System tutorial
  
  ,
  
   Kardi Teknomo's Tutorial
  
 
This tutorial is copyrighted .
Preferable reference for this tutorial is
Teknomo, Kardi (2015) Solving Ordinary Differential Equation (ODE). https:\\people.revoledu.com\kardi\ tutorial\ODE\
