TypeError: 'float' object has no attribute 'getitem' Python NBody Simulation

Question

I want to make N-Body simulation using Hermite Algorithm, but when I write this code, I keep getting an error, that said:

TypeError: 'float' object has no attribute '__getitem__'

and I have no idea why it's happen, because my object in list is not float.

dt    = input('dt = ')
t_end = input('t_end = ')
n = input('n= ')
t = input('t= ')

m = np.zeros(n)
r = np.zeros((n, 3))
rji = np.zeros((3))
vji = np.zeros((3))
v = np.zeros((n, 3))
a = np.zeros((n, 3))
jk = np.zeros((n, 3))


for i in range (0,n,1):
    m[i] = 2
    for k in range (0,3,1):
        r[i,k] = 2+i
    for k in range (0,3,1):
        v[i,k] = 1+i
    print ('m'),m,r,v


for i in range (0,n,1):
    for k in range (0,3,1):
        a[i,k] = jk[i,k] = 0.0
for i in range (0,n,1):
    for j in range (i+1,n,1):
        for k in range (0,3,1):
            rji[k] = r[j,k] - r[i,k]
            vji[k] = v[j,k] - v[i,k]


    r2 = 0.
    for k in range (0,3,1):
        r2 += rji[k] * rji[k]
    r3 = r2 * math.sqrt(r2)
    rv = 0.
    for k in range (0,3,1):
        rv += rji[k] * vji[k]
    rv /= r2
    for k in range (0,3,1):
        a[i,k] += m[j] * rji[k] / r3;
        a[j,k] -= m[i] * rji[k] / r3;
        jk[i,k] += m[j] * (vji[k] - 3 * rv * rji[k]) / r3;
        jk[j,k] -= m[i] * (vji[k] - 3 * rv * rji[k]) / r3;

ekin = 0.
epot = 0.

for i in range (0,n,1):
    for j in range (i+1,n,1):
        for k in range (0,3,1):
            rji[k] = r[j,k] - r[i,k] #the error coming from this line

    r2=0.
    for k in range (0,3,1):
        r2 += rji[k] * rji[k]
        print rji
    r = math.sqrt(r2)
    epot -= m[i] * m[j] / r
for k in range (0,3,1):
    ekin += 0.5 * m[i] * v[i,k] *v[i,k]
e_in = ekin + epot
print('Initial total energy E_in = '), e_in

Look in your code and find line 71 and see if that helps you figure out your error. If not, reduce your code to a minimal example. 150 lines is a lot to expect people to comb through to find your error for you. — khelwood, Oct 14 '14 at 07:02
is this had an effect if the array variable is already used in the first loop, and then i use it again in another loop, but it is okay to overwrite the value from previous loop. — Muhammad Isnaenda Ikhsan, Oct 14 '14 at 07:27
Please do not vandalise your post. By posting your question here, you put it under public license. — Adriaan, Mar 13 '17 at 15:37

Warren Weckesser · Answer 1 · 2014-10-13T07:26:21.080

I'm not sure if this is the source of error that you are seeing, but you are missing a variable name in this line (last line of all the loops):

        ekin += 0.5 * m[i] * v[i][k] *[i][k]

That should be

        ekin += 0.5 * m[i] * v[i][k] * v[i][k]

A comment on your code: you are using 2-dimensional numpy arrays, so you can index them as, for example, v[i,k] instead of v[i][k]. That notation is much more efficient, and it's easier to read.

TypeError: 'float' object has no attribute '__getitem__' Python NBody Simulation

1 Answers1

TypeError: 'float' object has no attribute 'getitem' Python NBody Simulation