element of
Say it “is in / belongs to”
The thing on the left is a member of the set on the right.
Example
x is a list of 3 real numbers.
In code
x in SWhere you’ll see it in ML
Stating types and shapes: W ∈ ℝ^{m×n} tells you W's shape.
Don’t confuse it with
- epsilon A tiny positive number — or, in models, a noise term.
- subset Every element of the left set is also in the right set (they may be equal).
- not an element of The thing on the left is not in the set.
- real vector / matrix space ℝⁿ is the set of length-n real vectors; ℝ^{m×n} is the set of m-by-n real matrices. It tells you shape.