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Update README.md

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Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>
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numpy/slices_views/README.md
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@ -12,7 +12,7 @@ Sometimes we want to use or see only a part of the matrix. This can be done via
Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
## Reminder
## Reminder: 1-d slines
We assume N as the number of elements and 1d:​
@ -36,3 +36,47 @@ print(a[5:]) # -> [5 6 7 8 9]
print(a[:]) # -> [0 1 2 3 4 5 6 7 8 9]
print(a[...]) # -> [0 1 2 3 4 5 6 7 8 9]
```
* Negative values for start and stop are understood as N-\|start\| and N-\|stop\|
* N-1 is the last valid index. ​
* Thus A[-1] gives us the last element of A.​
Extracting a value based on a negative index:
```python
import numpy as np
a = np.arange(0, 10)
print(a[-1]) # -> 9
print(a[-2]) # -> 8
print(a[-9]) # -> 1
print(a[-10]) # -> 0
print(a[-11]) # IndexError: index -11 is out of bounds for axis 0 with size 10
```
Extracting a slice based on a negative stop point:
```python
import numpy as np
a = np.arange(0, 10)
print(a) # -> [0 1 2 3 4 5 6 7 8 9]
print(a[:-1]) # -> [0 1 2 3 4 5 6 7 8]
print(a[:-5]) # -> [0 1 2 3 4]
print(a[:-8]) # -> [0 1]
print(a[:-11]) # -> []
print(a[:-12]) # -> []
print(a[:-999]) # -> []
```
Extracting a slice based on a negative start point:
```python
import numpy as np
a = np.arange(0, 10)
print(a) # -> [0 1 2 3 4 5 6 7 8 9]
print(a[-3:-1]) # -> [7 8]
print(a[-1:-8]) # -> []
print(a[-9999:]) # -> [0 1 2 3 4 5 6 7 8 9]
```