erlang蒙特卡洛方法求Pi

两个参数R，N分别代表范围和试验次数。思想是正方形内接圆，往正方形上扔飞镖，落在圆内计数加一，最终拿计数和总试验次数作比。
R=1M，N=1M 结果3.143856,3.140464,3.141572,取平均为3.141964

代码如下

-module(ex7).-import(math,[sqrt/1,pow/2]).-import(rand,[uniform/1]).-compile([export_all]).index(0,[H|_T])->H;index(N,[_H|T])->index(N-1,T).distance(A,B)->sqrt(pow(index(0,A)-index(0,B),2)+pow(index(1,A)-index(1,B),2)).count(N,R)->count(N-1,R,distance([0,0],[uniform(R),uniform(R)])).count(0,R,D)when D<R ->1;count(0,_R,_D)->0;count(N,R,D)when D<R ->1+count(N-1,R,distance([0,0],[uniform(R),uniform(R)]));count(N,R,_caD)->count(N-1,R,distance([0,0],[uniform(R),uniform(R)])).calPi(R,N)->io:format("~w~n",[4*count(N,R)/N]).