Meaning of R, Q, Z, and N characters in math 數學中R, Q, Z, N的意義

R - real numbers 實數 -∞ ~ ∞, no imaginary part i 不含虛部 i

Q - rational numbers 有理數 may be represented as a ratio of p/q, where q ≠ 0.

Z - integers 整數 ... -3, -2, -1, 0, 1, 2, 3, ...

N - natural numbers 自然數 1, 2, 3, 4, ...

R 包含了 Q
Q 包含了 Z
Z 包含了 N

Figure of R, Q, Z, and N relationship

Example:

point sampling

x[n] = x(nT), n ∈ Z
n 屬於整數

參考資料

https://en.wikipedia.org/wiki/Rational_number#/media/File:Number-systems.svg