Numpy provides a `cross`

function for computing vector cross products. The cross product of vectors `[1, 0, 0]`

and `[0, 1, 0]`

is `[0, 0, 1]`

. Numpy tells us:

```
>>> a = np.array([1, 0, 0])
>>> b = np.array([0, 1, 0])
>>> np.cross(a, b)
array([0, 0, 1])
```

as expected.

While cross products are normally defined only for three dimensional vectors. However, either of the arguments to the Numpy function can be two element vectors. If vector `c`

is given as `[c1, c2]`

, Numpy assigns zero to the third dimension: `[c1, c2, 0]`

. So,

```
>>> c = np.array([0, 2])
>>> np.cross(a, c)
array([0, 0, 2])
```

Unlike `dot`

which exists as both a Numpy function and a method of `ndarray`

, `cross`

exists only as a standalone function:

```
>>> a.cross(b)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'numpy.ndarray' object has no attribute 'cross'
```

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