Alphabetical approach

Содержание и основные понятия

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Alterna · Chapter 27 · page 27.1
Alphabetical approach
The power of the alphabet, the weight of the symbol, the volume of the message.
Alphabetical approach
- measures information by the volume of the text, doesn't depend on the meaning. Each alphabet character carries the same number of bits.
GEF
PIF
OGE No. 1
EEG No. 4
Relationship to Chapter 26.
B
Chapter 26 "Phano condition"
We've been building codes with a variable length.
even
coding: All characters are coded by the same number of bits i = log2N.
01
Basic concepts
Power of alphabet N
is the number of different characters in the alphabet.
Information weight of symbol i
- number of bits per symbol:
i = log₂N
.
Message I
:
I = K × i
where K is the number of symbols in the text.
Examples
Russian alphabet (33 letters + space + signs E 64 characters): i = log2(64) =
6 bits
.
ASCII (256 characters): i = log2(256) =
8 bits
= 1 byte.
Text of 1,000 characters, alphabet 64: I = 1000 x 6 =
6,000 bits = 750 byte
.
02
Formulas
Formula
Meaning
Application
i = log₂N
Weight of one symbol in bits
Dano N ♪ find i ♪
N = 2
i
Capability of alphabet at weight i
Dano i ♪ find N
I = K × i
Messages from K Symbols
K and i find I
K = I / i
Number of characters with known volume
Dano I and i ♪ find K
03
Volume calculator
🔢
Compute the message volume
Power of alphabet N
Number of characters K
Введите значения и нажмите «Вычислить».
04
Units for measuring information
The result of the calculation is in
bats
For translation:
1 byte = 8 bits
1 Kbyte = 1024 bytes = 81992 bits
1 Mbyte = 1024 Kbyte
Review of the OGE Model Task
Condition:
Alphabet contains 32 characters. Text of 120 characters. What is the information volume of the text in bytes?
Decision:
i = log2(32) = 5 bits (in symbol)
I = 120 x 5 = 600 bits
600 bits 8 =
75 byte
05
Text analyser
🔬
Put in any text, learn the volume.
Символов
—
UTF-16 (Windows)
—
16 бит/символ
KOI-8 / ASCII
—
8 бит/символ
7-бит ASCII
—
7 бит/символ
Top 10 characters by frequency
06
The Tasks Randommaster of the OGE
🎲
Trainer: Challenges on the volume of information
Generates random tasks in OGE No. 1 to calculate the volume of the text.
07
Guess the coding.
🕵️
Detective: by weight, define the coding
You're given the size of the file and the number of symbols.
Нажми «Новая задача» для начала.
🎯
Mini-test: 5 questions
XP: 0
🧩
Check yourself out.
5 questions in alphabetical approach · 20 XP for each correct answer