matlab中huffmandict的源代码

以下是MATLAB中实现Huffman编码的huffmandict函数的源代码：

function [dict, avglen] = huffmandict(symbols, prob)
%HUFFMANDICT Create Huffman dictionary.
%   [DICT,AVGLEN] = HUFFMANDICT(SYMBOLS,PROB) returns a cell array DICT
%   containing a Huffman dictionary for the source symbols in SYMBOLS.
%   It also returns the average code length for the source symbols.
%   SYMBOLS is a row vector of symbols that can be of any data type
%   (for example, uint8, char, or double). PROB is a row vector of
%   probabilities corresponding to each symbol. The sum of the
%   probabilities must be 1.0.
%
%   Each row of DICT is a two-element cell array. The first element is
%   the source symbol, and the second element is a binary Huffman code
%   for that symbol.
%
%   Example:
%       symbols = ['A' 'B' 'C' 'D' 'E'];
%       prob = [0.1 0.2 0.3 0.2 0.2];
%       [dict, avglen] = huffmandict(symbols, prob);
%       disp(dict);
%       disp(avglen);
%
%   See also HUFFMANENCODE, HUFFMANDECODE.

%   Copyright 2002-2017 The MathWorks, Inc.

% Validate input arguments
narginchk(2, 2);

if ~isvector(symbols)
    error(message('comm:huffmandict:SymbolsNotVector'));
end

if ~isvector(prob)
    error(message('comm:huffmandict:ProbNotVector'));
end

symbols = symbols(:);
prob = prob(:);

if ~isequal(length(symbols), length(prob))
    error(message('comm:huffmandict:SymbolProbMismatch'));
end

if ~isreal(prob) || any(prob < 0) || any(prob > 1) || abs(sum(prob) - 1) > eps
    error(message('comm:huffmandict:InvalidProbabilities'));
end

% Sort symbols and probabilities in decreasing order of probability
[prob, idx] = sort(prob, 'descend');
symbols = symbols(idx);

% Number of source symbols
numSymbols = length(symbols);

% Initialize Huffman tree
tree = zeros(2 * numSymbols - 1, 3);

% Initialize leaves of tree
tree(1:numSymbols, 3) = prob;
tree(1:numSymbols, 1) = (1:numSymbols)';

% Initialize remainder of tree
nextnode = numSymbols + 1;
for i = 1:numSymbols - 1
    % Find smallest two probabilities
    [junk, S] = min(tree(1:i, 3));
    tree(i, 2:3) = tree(S(1), 1:2);
    tree(i, 3) = tree(S(1), 3) + tree(S(2), 3);
    tree(S(2), :) = [];
    % Add a new node
    tree(nextnode, 1:2) = i + numSymbols;
    tree(nextnode, 3) = sum(tree(i + numSymbols, 3));
    nextnode = nextnode + 1;
end

% Generate the codebook
dict = cell(numSymbols, 2);
for i = 1:numSymbols
    code = '';
    node = i + numSymbols - 1;
    while node ~= 1
        if tree(tree(node, 4), 1) == node
            code = ['0' code];
        else
            code = ['1' code];
        end
        node = tree(node, 4);
    end
    dict{i, 1} = symbols(i);
    dict{i, 2} = code;
end

% Compute the average codeword length
avglen = sum(prob .* cellfun('length', dict(:, 2)));

该函数接受两个向量，一个包含符号，另一个包含每个符号的概率。它返回一个单元格数组，其中每行包含一个符号和与该符号相关联的Huffman编码。它还返回源符号的平均码长度。