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HW3/Q3.cpp

+#include "mpi.h" 
+#include <stdio.h> 
+#include <iostream>
+#include <stdlib.h>
+#include <algorithm>sort
+
+void parallel_search(double Guess, bool flag, double &Array){
+	int myRank;
+	MPI_Comm_rank(MPI_COMM_WORLD, &myRank);
+
+	int lesscount=0;
+	int largercount=0;
+    
+    double threshold=1;
+    double Granular=0.1;
+    
+    int SubSize=ArraySize/nProcs;
+    double *SubArray=new double[SubSize];
+    
+    initilize_SubArray(myRank,&SubArray,&Array);//assume there's a function to initialize
+    
+    sort(SubArray,SubArray+SubSize);
+    //counting
+	for(int i=0;i<SubSize;i++){
+		if SubArray[i]<=Guess
+			lesscount++;
+		if SubArray[i]>Guess
+			largercount++;
+	}
+    
+    int LessGlobal=0;
+    int LargerGlobal=0;
+    MPI_Reduce(&lesscount,&LessGlobal,1,MPI_INT,MPI_SUM,0,MPI_COMM_WORLD);
+    MPI_Reduce(&lagercount,&LargerGlobal,1,MPI_INT,MPI_SUM,0,MPI_COMM_WORLD);
+
+   if(!myRank){
+        if(LessGlobal-LargerGlobal>=threshold)
+    		Guess=Guess-Granular;
+ 		if(LargerGlobal-LessGlobal>=threshold)
+    	    Guess=Guess+Granular;    
+    	if(abs(LessGlobal-LargerGlobal)<threshold)
+    		flag=false;
+    }
+
+  }  
+
+
+int main(){
+	int nProcs;
+	int myRank;
+	MPI_Init(NULL, NULL);
+	MPI_Comm_size(MPI_COMM_WORLD, &nProcs);
+	MPI_Comm_rank(MPI_COMM_WORLD, &myRank);
+    
+    int ArraySize=10000;
+  
+    double *Array=new double[ArraySize];
+    
+    double Guess=rand();
+    bool flag=true;
+    
+    do{
+    parallel_search(Guess, flag, &Array);   	
+    }while(flag);
+
+   if(!myRank){
+   	cout<<"The median is "<<Guess<<endl;
+   }
+
+ 	MPI_Finalize();
+	return 0;
+}
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