c - rand() 不返回随机值

Question

生成随机厄密矩阵的小代码hermitian matrix .

我在每次调用 rand() 之前调用了 srand()。但输出仍然没有随机性。

我已经使用 c99 的复杂数据类型功能创建了厄尔米特矩阵。我不确定我哪里错了:(

#include <stdio.h>
#include <math.h>
#include <complex.h>
#include <stdlib.h>
#include <time.h>

#define MATSIZE 5
#define RAND_RANGE 100

double complex mat[MATSIZE][MATSIZE];

void gen_mat()
{
  int i =0,j;
  int real;
  int img;
  for( ;i < MATSIZE; i++)
  {
    srand(time(NULL));
    real = rand()%RAND_RANGE + 1;
    srand(time(NULL));
    img = rand()%RAND_RANGE + 1;
    for(j = MATSIZE; j != i ; j--) 
    { 
       mat[i][j] = real + img * I;
       mat[j][i] = conj(mat[i][j]);
    }
    srand(time(NULL));
    if(i == j)
      mat[i][i] = rand()%RAND_RANGE + 0*I;
  }
}

void print_mat()
{
  int i,j;
  for(i = 0; i < MATSIZE; i++)
  {
    for(j = 0; j < MATSIZE; j++)
    {
      printf("%f + %f *i", creal(mat[i][j]), cimag(mat[i][j]));
      printf("    ");
    }
    puts("\n");
  }
}

int main()
{
  gen_mat();
  print_mat();
  return 0;
}

示例输出

[aft@centos-c physics-numaric]$ ./a.out 
66.000000 + 0.000000 *i    67.000000 + 67.000000 *i    67.000000 + 67.000000 *i             67.000000 + 67.000000 *i    67.000000 + 67.000000 *i    

67.000000 + -67.000000 *i    66.000000 + 0.000000 *i    67.000000 + 67.000000 *i      67.000000 + 67.000000 *i    67.000000 + 67.000000 *i    

67.000000 + 67.000000 *i    67.000000 + -67.000000 *i    66.000000 + 0.000000 *i    67.000000 + 67.000000 *i    67.000000 + 67.000000 *i    

67.000000 + 67.000000 *i    67.000000 + -67.000000 *i    67.000000 + -67.000000 *i    66.000000 + 0.000000 *i    67.000000 + 67.000000 *i    

67.000000 + 67.000000 *i    67.000000 + -67.000000 *i    67.000000 + -67.000000 *i      67.000000 + -67.000000 *i    66.000000 + 0.000000 *i    

编辑在 main() 中调用 srand 实际上解决了问题。谢谢你们。

[aft@centos-c physics-numaric]$ ./a.out 
31.000000 + 0.000000 *i    81.000000 + 75.000000 *i    81.000000 + 75.000000 *i     81.000000 + 75.000000 *i    81.000000 + 75.000000 *i    

81.000000 + -75.000000 *i    53.000000 + 0.000000 *i    69.000000 + 57.000000 *i    69.000000 + 57.000000 *i    69.000000 + 57.000000 *i    

69.000000 + 57.000000 *i    69.000000 + -57.000000 *i    27.000000 + 0.000000 *i    93.000000 + 11.000000 *i    93.000000 + 11.000000 *i    

93.000000 + 11.000000 *i    69.000000 + -57.000000 *i    93.000000 + -11.000000 *i    58.000000 + 0.000000 *i    76.000000 + 78.000000 *i    

76.000000 + 78.000000 *i    69.000000 + -57.000000 *i    93.000000 + -11.000000 *i    76.000000 + -78.000000 *i    67.000000 + 0.000000 *i    

Answer 1

不要在每次调用 rand 之前调用 srand。程序启动时调用一次。