# python – IndexError: index out of bounds

## python – IndexError: index out of bounds

From a quick look, it seems the problem is the for loop, instead of using `for i in [N[0]]`

, are you sure its not `for i in range(N[0])`

?

`for i in [N[0]]`

is rather redundant because the list only contains one element, ie. `N[0]`

, so the list of size **800** becomes out of index when you try to seek `dydt[800]`

<– as the max index is `799`

.

Like so:

```
In [9]: N
Out[9]: [800, 400, 800]
In [10]: for i in [N[0]]: # ie. i == N[0] == 800
....: dydt[i] = 0
....:
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
<ipython-input-10-04daa45ec403> in <module>()
1 for i in [N[0]]: # ie. i == N[0] == 800
----> 2 dydt[i] = 0
3
IndexError: index 800 is out of bounds for axis 0 with size 800
In [11]: for i in range(N[0]):
....: dydt[i] = 0
....:
```

```
L = [8.0, 4.0, 8.0]
dN = 1.0e2
N = [int(l*dN) for l in L] # create array [800, 400, 800]
dydt = np.zeros(shape=N) # create 3 dimensional matrix
# 1d has size 800 (from 0 to 799 including)
# 2d has size 400 (from 0 to 399 including)
# 3d same as 1st
```

In this code:

```
for i in[N[0]]:
dydt[i] = 0 # Unknown point
```

I is always 800 so it actually same as `dydt[ 800 ] = 0`

. which is bigger then 799.

Its looks like that you use numpy arrays in wrong way.

Yes in low level they represents as contiguous array of ints or floats of whatever. But on python level np.array represents as array of arrays. (ie first element as 3d matrix `mtx = np.zeros(shape=[800,400,800]`

in python will be `mtx[0][0][0]`

)).

So all code after `for i in[N[0]]:`

will not work. It tries to access subarray that out of matrix bounds.

UPDATE:

for example you have 3d matrix (3x3x3)

```
mtx=np.zero(shape=[3,3,3])
print(mtx)
#[ [ [ 0. 0. 0.]
# [ 0. 0. 0.]
# [ 0. 0. 0.] ]
# [ [ 0. 0. 0.]
# [ 0. 0. 0.]
# [ 0. 0. 0.] ]
# [ [ 0. 0. 0.]
# [ 0. 0. 0.]
# [ 0. 0. 0.] ] ]
mtx[0] = 1
print( mtx )
#[ [ [ 1. 1. 1.]
# [ 1. 1. 1.]
# [ 1. 1. 1.] ]
# [ [ 0. 0. 0.]
# [ 0. 0. 0.]
# [ 0. 0. 0.] ]
# [ [ 0. 0. 0.]
# [ 0. 0. 0.]
# [ 0. 0. 0.] ] ]
mtx[0][1] = 2
#[ [ [ 1. 1. 1.]
# [ 2. 2. 2.]
# [ 1. 1. 1.] ]
# others are zeros
mtx[0][1][2] = 3
#[ [ [ 1. 1. 1.]
# [ 2. 2. 3.]
# [ 1. 1. 1.] ]
# others are zeros
```