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Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>
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numpy/broadcasting/README.md
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@ -14,7 +14,7 @@ Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
## [General broadcasting rules](https://numpy.org/devdocs/user/basics.broadcasting.html) ## [General broadcasting rules](https://numpy.org/devdocs/user/basics.broadcasting.html)
> When operating on two arrays, NumPy compares their shapes element-wise. It starts with the trailing (i.e. rightmost) dimension and works its way left. **Two dimensions are compatible when** > When operating on two arrays, NumPy compares their shapes element-wise. It starts with the trailing (i.e. ***rightmost***) dimension and works its way left. **Two dimensions are compatible when**
> >
> * **they are equal**, or > * **they are equal**, or
> * **one of them is 1**. > * **one of them is 1**.
@ -40,3 +40,47 @@ Figure 3 (from [numpy.org](https://numpy.org/devdocs/user/basics.broadcasting.ht
Figure 4 (from [numpy.org](https://numpy.org/devdocs/user/basics.broadcasting.html)) : In some cases, broadcasting stretches both arrays to form an output array larger than either of the initial arrays. Figure 4 (from [numpy.org](https://numpy.org/devdocs/user/basics.broadcasting.html)) : In some cases, broadcasting stretches both arrays to form an output array larger than either of the initial arrays.
## [Examples](https://numpy.org/devdocs/user/basics.broadcasting.html#broadcastable-arrays)
Good:
```python
Image (3d array): 256 x 256 x 3
Scale (1d array): 3
Result (3d array): 256 x 256 x 3
A (4d array): 8 x 1 x 6 x 1
B (3d array): 7 x 1 x 5
Result (4d array): 8 x 7 x 6 x 5
A (2d array): 5 x 4
B (1d array): 1
Result (2d array): 5 x 4
A (2d array): 5 x 4
B (1d array): 4
Result (2d array): 5 x 4
A (3d array): 15 x 3 x 5
B (3d array): 15 x 1 x 5
Result (3d array): 15 x 3 x 5
A (3d array): 15 x 3 x 5
B (2d array): 3 x 5
Result (3d array): 15 x 3 x 5
A (3d array): 15 x 3 x 5
B (2d array): 3 x 1
Result (3d array): 15 x 3 x 5
```
Bad:
```python
A (1d array): 3
B (1d array): 4 # trailing dimensions do not match
A (2d array): 2 x 1
B (3d array): 8 x 4 x 3 # second from last dimensions mismatched
```