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Help in Python rk4

  1. Feb 19, 2009 #1
    i have been attempting to plot a first order ODE with pyhton's rk4

    i can't display the graph and i have been having this error:

    Traceback (most recent call last):
    File "C:\Documents and Settings\AP155user38\Desktop\gladys python codes\differential equations and runge-kutta\1ODE.py", line 20, in <module>
    Y[i+1] = rk4(t, Y, f)
    File "c:\python25\lib\site-packages\matplotlib-0.98.3.0001-py2.5-win32.egg\matplotlib\mlab.py", line 928, in rk4
    yout = np.zeros( (len(t),), np.float_)
    TypeError: object of type 'function' has no len()

    i need help in understanding this so i could move on with solving the error. :)

    i hope you guys could help me out.

    here's my code:

    from scipy import *
    from pylab import *


    h = 0.1 #time step
    ti = 0. #start
    tf = 10. #end
    t = arange(ti, tf, h) #time array

    N = len(t) #number of time steps
    Y = zeros(N) #stores value of y at each time step

    Y[0] = 0. #initial condition

    def f(t, Y):
    dYdt = -9.81 - 0.5*Y
    return dYdt

    for i in range(N-1):
    Y[i+1] = rk4(t, Y, f)

    plot(t,Y)
    show()

    thanx.

    gulaman
    Quezon City, Philippines
     
  2. jcsd
  3. Mar 1, 2009 #2
    I don't use Python but I had "learned" it enough to pass a class.

    I think you're getting the error because you're not passing any arguments to f for rk4 to use.

    Or

    The value of t or Y is a null value.

    Hope that helps. :-/
     
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