Runge Kutta 4th Order Method

05302015, 06:03 PM
(This post was last modified: 05302015 06:05 PM by Eddie W. Shore.)
Post: #1




Runge Kutta 4th Order Method
The Runge Kutta 4th Order is a method for solving differential equations involving the form: dy/dx = f(x,y), where:
x_n+1 = x_n + h y_n+1 = y_n + (k1 + 2*k2 + 2*k3 + k4)/6 Where: k1 = h * f(x_n, y_n) k2 = h * f(x_n + h/2, y_n + k1/2) k3 = h * f(x_n + h/2, y_n + k2/2) k4 = h * f(x_n + h, y_n + k3) Variables used: A = x_n B = y_n C = x_n+1 D = y_n+1 H = step K = k1 L = k2 M = k3 N = k4 Results are stored in lists L1 and L2. L1 represents the x coordinates, L2 represents the y coordinates. Both DIFFTBL and RK4 return the same output. The difference is that DIFFTBL uses an Input box and nopass through arguments and RK4 uses five passthrough arguments. This way, RK4 could be used as a subroutine. Both return the results in a matrix, M1. DIFFTBL: Code: EXPORT DIFFTBL() RK4: Code: EXPORT RK4(f,A,B,H,S) 

10102015, 12:32 AM
Post: #2




RE: Runge Kutta 4th Order Method
How do you use the RK4 program..not using it as a subroutine..so it
gives the same output as DIFFTBL..what do you use for f? when running from the program menu for example...if you use 'X' (where dy/dx = X = f) it really doesn't return the correct values to the M1..humm..maybe it is written only for a subroutine..? thanks E 

10102015, 02:41 PM
Post: #3




RE: Runge Kutta 4th Order Method
Ok, if you add a definition of f (the function you want) say f='X' in the RK4 code then I can run the RK4 to get the same and correct response as DFFTBL.
E 

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