Maths for ML / Notation

a \times b

times / dimension

Arithmetic and relationsBeginner

Say it “times / by”

Ordinary multiplication — or, between sizes, 'by' as in a 3 × 4 matrix.

Example

3\times 4

In code

a * b

Where you’ll see it in ML

Writing shapes: an image is 224 × 224 × 3.

Don’t confuse it with

$\mathbf{a}\cdot\mathbf{b}$ dot product Multiply matching entries and add them up. Gives one number that's large when the vectors point the same way.
$\mathbf{a}\times\mathbf{b}$ cross product (3-D) For two 3-D vectors, gives a vector perpendicular to both.
$A \times B$ Cartesian product All ordered pairs with the first from A and the second from B.

Lessons that use it

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