MATLAB中的互信息计算

function MIhat = nmi（ A B ） 
    %NMI Normalized mutual information
    % http://en.wikipedia.org/wiki/Mutual_information
    % http://nlp.stanford.edu/IR-book/html/htmledition/evaluation-of-clustering-1.html

    % Author: http://www.cnblogs.com/ziqiao/   [2011/12/13] 

    if length（ A ） ~= length（ B）
        error（‘length（ A ） must == length（ B）‘）;
    end
    total = length（A）;
    A_ids = unique（A）;
    B_ids = unique（B）;

    % Mutual information
    MI = 0;
    for idA = A_ids
        for idB = B_ids
             idAOccur = find（ A == idA ）;
             idBOccur = find（ B == idB ）;
             idABOccur = intersect（idAOccuridBOccur）; 

             px = length（idAOccur）/total;
             py = length（idBOccur）/total;
             pxy = length（idABOccur）/total;

             MI = MI + pxy*log2（pxy/（px*py）+eps）; % eps : the smallest positive number

        end
    end

    % Normalized Mutual information
    Hx = 0; % Entropies
    for idA = A_ids
        idAOccurCount = length（ find（ A == idA ） ）;
        Hx = Hx - （idAOccurCount/total） * log2（idAOccurCount/total + eps）;
    end
    Hy = 0; % Entropies
    for idB = B_ids
        idBOccurCount = length（ find（ B == idB ） ）;
        Hy = Hy - （idBOccurCount/total） * log2（idBOccurCount/total + eps）;
    end

    MIhat = 2 * MI / （Hx+Hy）;
end

 属性            大小     日期    时间   名称
----------- ---------  ---------- -----  ----
     目录           0  2015-05-31 10:57  nmi\
     文件      263222  2009-12-18 02:54  nmi\22.bmp
     文件      263222  2009-12-18 02:54  nmi\23.bmp
     文件      263222  2009-12-18 02:54  nmi\24.bmp
     文件      263222  2009-12-18 02:58  nmi\25.bmp
     文件      263222  2009-12-18 02:57  nmi\26.bmp
     文件      263222  2009-12-18 02:57  nmi\27.bmp
     文件        1365  2015-05-26 20:27  nmi\nmi.m
     文件        1129  2015-05-26 20:33  nmi\nmimem.m