我正在嘗試使用montecarlo方法和使用并行C代碼來查找PI的值。我已經(jīng)寫了serail代碼并且工作正常。但是，并行代碼給我一些時間0或PI錯誤的值負(fù)值使用蒙特卡洛方法多線程計算pi值

我的代碼

#include

#include

#include

#include

#define NUM_THREADS 4 //number of threads

#define TOT_COUNT 10000055 //total number of iterations

void *doCalcs(void *threadid)

{

long longTid;

longTid = (long)threadid;

int tid = (int)longTid; //obtain the integer value of thread id

//using malloc for the return variable in order make

//sure that it is not destroyed once the thread call is finished

float *in_count = (float *)malloc(sizeof(float));

*in_count=0;

unsigned int rand_state = rand();

//get the total number of iterations for a thread

float tot_iterations= TOT_COUNT/NUM_THREADS;

int counter=0;

//calculation

for(counter=0;counter

//float x = (double)random()/RAND_MAX;

//float y = (double)random()/RAND_MAX;

//float result = sqrt((x*x) + (y*y));

double x = rand_r(&rand_state)/((double)RAND_MAX + 1) * 2.0 - 1.0;

double y = rand_r(&rand_state)/((double)RAND_MAX + 1) * 2.0 - 1.0;

float result = sqrt((x*x) + (y*y));

if(result<1){

*in_count+=1; //check if the generated value is inside a unit circle

}

}

//get the remaining iterations calculated by thread 0

if(tid==0){

float remainder = TOT_COUNT%NUM_THREADS;

for(counter=0;counter

float x = (double)random()/RAND_MAX;

float y = (double)random()/RAND_MAX;

float result = sqrt((x*x) + (y*y));

if(result<1){

*in_count+=1; //check if the generated value is inside a unit circle

}

}

}

}

int main(int argc, char *argv[])

{

pthread_t threads[NUM_THREADS];

int rc;

long t;

void *status;

float tot_in=0;

for(t=0;t

rc = pthread_create(&threads[t], NULL, doCalcs, (void *)t);

if (rc){

printf("ERROR; return code from pthread_create() is %d\n", rc);

exit(-1);

}

}

//join the threads

for(t=0;t

pthread_join(threads[t], &status);

//printf("Return from thread %ld is : %f\n",t, *(float*)status);

tot_in+=*(float*)status; //keep track of the total in count

}

printf("Value for PI is %f \n",1, 4*(tot_in/TOT_COUNT));

/* Last thing that main() should do */

pthread_exit(NULL);

}

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該代碼中有許多可疑的事情，比如為什么你為'in_count'動態(tài)地分配一個浮點(diǎn)數(shù)？你順便把它看作一個整數(shù)。哦，而且你并沒有在任何地方釋放導(dǎo)致內(nèi)存泄漏的配置。 –

+0

我建議使用'double'。如果你想'浮動'，為什么不計算'22/7'或'355/113'？ –

+0

@WeatherVane他想嘗試蒙特卡洛方法，我認(rèn)為教育。 –

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