Maths for ML / Notation

\mathbf{a}\times\mathbf{b}

cross product (3-D)

Linear algebraAdvanced

Say it “a cross b”

For two 3-D vectors, gives a vector perpendicular to both.

Example

\hat{x}\times\hat{y}=\hat{z}

In code

np.cross(a, b)

torch.linalg.cross(a, b)

Where you’ll see it in ML

Robotics, 3-D vision, rotations — rare in standard deep learning.

Don’t confuse it with

$a \times b$ times / dimension Ordinary multiplication — or, between sizes, 'by' as in a 3 × 4 matrix.
$\mathbf{a}\cdot\mathbf{b}$ dot product Multiply matching entries and add them up. Gives one number that's large when the vectors point the same way.
$A \times B$ Cartesian product All ordered pairs with the first from A and the second from B.

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