Entropy of a discrete random variable with possible values {π‘₯1,π‘₯2,…,π‘₯𝑛}…

2017

Entropy of a discrete random variable with possible valuesΒ {π‘₯1,π‘₯2,…,π‘₯𝑛}Β and probability density function 𝑃(𝑋)Β is

\(H(X) = \: – \sum\limits_{i=1}^{n}P(x_i) \log _bP(x_i)\)

The value of 𝑏 gives the units of entropy. The unit for 𝑏 = 10Β is

  1. A.

    bits

  2. B.

    bann

  3. C.

    nats

  4. D.

    deca

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Show answer & explanation

Correct answer: B

Answer: The unit for base 10 is the ban (also called the hartley or decimal digit).

Explanation: The base of the logarithm in the entropy formula determines the unit of information. Common mappings are:

  • Base 2 β†’ bits

  • Base e (natural log) β†’ nats

  • Base 10 β†’ bans (also called hartleys or decimal digits)

Useful conversions:

  • 1 ban β‰ˆ log2(10) β‰ˆ 3.3219 bits

  • 1 nat β‰ˆ log2(e) β‰ˆ 1.4427 bits

Therefore, when b = 10 in the entropy formula, the unit is the ban (hartley).

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