计算信息熵的简单做法

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信息熵的简单做法

p*log(p)其中log函数是以2为底的函数，在C语言中，计算概率是可以应用换底公式来计算上面的公式。
直接贴代码了：

#include <map>#include <cmath>#include <iostream>#include <string>#include <stdio.h>int GetSumCnt(std::map<std::string, int> &smap){    int cnt_sum = 0;    std::map<std::string, int>::iterator iter;    for(iter = smap.begin(); iter != smap.end(); ++ iter)        cnt_sum += iter->second;    return cnt_sum;}int main(){    float score = 0.0, p_tmp = 0.0;    int cnt = 0;    int cnt_sum = 0;    std::string str;    std::map<std::string, int> smap;    std::map<std::string, int>::iterator iter;    str = "baidu";    cnt = 3;    smap[str] += cnt;    score = 0.0;    cnt_sum = GetSumCnt(smap);    for(iter = smap.begin(); iter != smap.end(); ++ iter)    {        p_tmp = ((float)iter->second) / ((float)cnt_sum);        printf("The p_tmp is %f\n", p_tmp);        score -= p_tmp * (log(p_tmp) / log(2));    }    printf("The score is %f\n", score);    str = "beijing";    cnt = 3;    smap[str] += cnt;    score = 0.0;    cnt_sum = GetSumCnt(smap);    for(iter = smap.begin(); iter != smap.end(); ++ iter)    {        p_tmp = ((float)iter->second) / ((float)cnt_sum);        printf("The p_tmp is %f\n", p_tmp);        score -= p_tmp * (log(p_tmp) / log(2));    }    printf("The score is %f\n", score);    str = "beijing";    cnt = 3;    smap[str] += cnt;    score = 0.0;    cnt_sum = GetSumCnt(smap);    for(iter = smap.begin(); iter != smap.end(); ++ iter)    {        p_tmp = ((float)iter->second) / ((float)cnt_sum);        printf("The p_tmp is %f\n", p_tmp);        score -= p_tmp * (log(p_tmp) / log(2));    }    printf("The score is %f\n", score);    return 0;}

在此，主要想记录的是换底公式，在写代码的时候，可以让代码更加方便简洁一些。

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