how to capture variables and and store them in an array?

[ritesh247]

Lets say for this function:
x=5
z=10
for i in range (200):
V= i*z*x

how would i be able to capture all the values of V in the range 200 (make an array, as i have tried making it but i have gotten no where) and calculate its mean??

2) If I am supposed to create a probability density function..how can I create one using python??

[bvdet]

Question 1
The easiest way is to generate a list with a list comprehension.

>>> [i*5*10 for i in range(10)]
[0, 50, 100, 150, 200, 250, 300, 350, 400, 450]
>>>

Question 2
Your question is vague. A function can be created for just about any task. Anyway, I don't know the mathematics. Ask me about trigonometry or algebra though.

An example of a function that calculates an average of a list of numbers:

>>> def avg(seq):
... 	return sum(seq)/float(len(seq))
... 
>>> avg([i*5*10 for i in range(10)])
225.0
>>>

[ritesh247]

I am trying all those steps but am still not getting the required results, I am attaching my script code. Could you please have a look at it and tell me why am not being able to store the variables in a list. Since I want to calculate the mean of Vf. When i try getting the mean for Vf i gt the same value as Vf and thts not the correct answer:

for carlo in range (20): # Initially carrying out in the range from 0 to 20
    s = 7.5
    c = 2.0
    m = 100.0
    theta_freq = 10
    a = 2*math.pi
    rho = 1.225
    Mthetadot = -1.2
    xcm = 0.5*c
    xf = 0.48*c
    e = xf/c-0.25

    def kappa_freq(a, b):                                            # function for generating random variable
        return a+(b-a)*np.random.uniform()
    kappa_freqrn= kappa_freq(4.5, 5.5)
    #print "kappa_freqrn=", kappa_freqrn

    vel   = zeros((2501,1),float)
    freq1 = zeros((2501,1),float)
    freq2 = zeros((2501,1),float)
    freq3 = zeros((2501,1),float)
    freq4 = zeros((2501,1),float)
    damp1 = zeros((2501,1),float)
    damp2 = zeros((2501,1),float)
    damp3 = zeros((2501,1),float)
    damp4 = zeros((2501,1),float)

    vstart = 1.0
    vinc = 0.1
    for icount in range(1751):            # velocity loop
    
        V=vstart + icount*vinc
        a11 = (m*s*s*s*c)/3.0
        a22 = m*s*(c*c*c/3.0-c*c*xf+xf*xf*c)
        a12 = m*s*s*(c*c/2.0-c*xf)/2.0
        a21 = a12
        A = matrix([[a11,a21],[a12,a22]])
        Ainv = linalg.inv(A)



        k1 = ((kappa_freqrn*a)**2)*a11
        k2 = ((theta_freq*a)**2)*a22

        rv = rho*V
        c11 = rv*c*s*s*s*a/6.0
        c12 = 0.0
        c21 = -rv*c*c*s*s*e*a/4.0
        c22 = -rv*c*c*c*s*Mthetadot/8.0
        C = matrix([[c11,c12],[c21,c22]])
        AC = -Ainv*C

        rv2 = rho*V*V
        k11 = k1
        k12 = rv2*c*s*s*a/4.0
        k21 = 0.0
        k22 = k2 - rv2*c*c*s*e*a/2.0
        K = matrix([[k11,k12],[k21,k22]])
        AK = -Ainv*K

        temp = concatenate((AK,AC),axis=1)
        M = concatenate((matrix([[0.0,0.0,1.0,0.0],[0.0,0.0,0.0,1.0]]),temp),axis=0)

        Meig = linalg.eig(M)[0]


        vel[icount] = V
        freq1[icount] = abs(Meig[0])
        damp1[icount] = -100.0*real(Meig[0])/freq1[icount]
        freq1[icount] = freq1[icount]/a
        freq2[icount] = abs(Meig[1])
        damp2[icount] = -100.0*real(Meig[1])/freq2[icount]
        freq2[icount] = freq2[icount]/a
        freq3[icount] = abs(Meig[2])
        damp3[icount] = -100.0*real(Meig[2])/freq3[icount]
        freq3[icount] = freq3[icount]/a    
        freq4[icount] = abs(Meig[3])
        damp4[icount] = -100.0*real(Meig[3])/freq4[icount]
        freq4[icount] = freq4[icount]/a

        if damp3[icount] < 0:          
            break



    ab = (damp3[icount-1])
    #print ab 

    bc = (damp3[icount])
    #print bc

    Vf_min = V-0.1
    #print 'Vf_min=', Vf_min

    Vf_max = V
    #print 'Vf_max=', Vf_max



    def flutter_speed(ab,bc,Vf_min,Vf_max):                 # flutter_speed function
        return (Vf_min+(Vf_max - Vf_min)*(-(ab)/(bc - ab)))
    Vf = flutter_speed(ab,bc,Vf_min,Vf_max)
    print Vf
    Vf1 = [Vf_max for i in range(carlo)]
    print Vf1

I want to calculate the mean of Vf1...hw can i do tht?? I would appreciate all your help

[bvdet]

Please use code tags when posting code. See posting guidelines here.

Before the for loop, initialize an empty list.

outputList = []

At the end of your code:

    Vf = flutter_speed(ab,bc,Vf_min,Vf_max)
    outputList.append(Vf[0])
    
print sum(outputList)/len(outputList)

[ritesh247]

I will make sure I will use the code tags when posting code.
I tried implementing the method you wrote down but it gives me the same results as before. I am trying to print out the mean velocity all its giving me is the velocity which is the last Vf it prints out. I am wondering if this problem can be solved. Really sorry for asking so many questions.

[ritesh247]

Got it working thanks :)

but now when i try making a list for Vf_min anf Vf_max i get this error:
Type Error: 'float' object is unsubscriptable

why do i get such an error??

[bvdet]

In the code I commented on, Vf was a single element array. You must be attempting the same thing on a float, which gives you the error.

>>> Vf
array([ 157.88112949])
>>> Vf[0]
157.88112949000001
>>>