bayes.cpp

运筹学中的贝叶斯决策方法

#include <stdio.h>
#include <math.h>

#define pi 3.14159
#define p(x,t) exp(-(x-t)*(x-t)/20)/sqrt(20*pi)

void decision(){
 int i,j,type,m,n,flag,state[5],index;
 float xx,a[5][5],p[5],e[5],sum,decision;
 printf("Welcome to the DECISION_STSTEM!");
 printf(" type of the problem,max(key ?0?)or min(key ?1?)?   ");
 scanf("%d",&type);
 printf("type of the decision,without data(key?0?)or with data(key?1?)?   ");
 scanf("%d",&flag);
 printf("number of the actions   ");
 scanf("%d",&m);
 printf("number of the nature states    ");
 scanf("%d",&n);
 for(j=0;j<n;j++)
  printf(" t%d",j+1);
 printf(" ");
 for(i=0;i<m;i++)
  {printf("A%d ",i+1);
  for(j=0;j<n;j++)
   scanf("%f",&a[i][j]);
  }
 printf("probability of the natural states=? ");
 for(j=0;j<n;j++)
  scanf("%f",&p[j]);
 if(flag)
  {printf("given data=?   ");
  scanf("%f",&xx);
  printf("states of nature=? ");
  for(j=0;j<n;j++)
   scanf("%d",&state[j]);
  sum=0;
  for(j=0;j<n;j++)
   sum+=p[j]*p(xx,state[j]);
  for(j=0;j<n;j++)
   p[j]=p[j]*p(xx,state[j])/sum;
  }
 for(i=0;i<m;i++)
  {sum=0;
  for(j=0;j<n;j++)
   sum+=p[j]*a[i][j];
  e[i]=sum;
  }
 decision=e[0];
 index=1;
 if(type==0)
  for(i=1;i<m;i++)
  { if(decision<e[i])
    {decision=e[i];
    index=i+1;
    }
  }
 else
  for(i=0;i<m;i++)
   if(decision>e[i])
    {decision=e[i];
    index=i+1;
    }
 printf(" ********** ");
 printf("Results:");
 printf(" ********** ");
 printf("expected loss for each course of action based on prior distribution ");
 for(i=0;i<m;i++)
  printf("%f ",e[i]);
 printf(" The optimum expected loss is %f       ",decision);
 printf(" choose action A( %d )",index);
 return;
}

void main(){
 clrscr();
 decision();
 getch();
}