rand（）不返回随机值 [英] rand() is not returning random values

问题描述

它是一个小代码，用于生成一个随机Hermitian矩阵。

在每次调用rand（）之前，我都调用了srand（）。但输出中仍然没有随机性。

我使用c99的复杂数据类型功能来创建厄米特矩阵。我不确定我错在哪里：（$ / b>

  #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（）
 {
; 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  {
 for（j = 0; j  {
 print f（％f +％f * i，creal（mat [i] [j]），cimag（mat [i] [j]））; 
 printf（）; 
} 
 puts（\\\
）; 
 
 
 
 int main（）
 {
 gen_mat（）; 
 print_mat（）; 
返回0; 
} 
  

样本输出

<$ $ ./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

在main（）中调用srand的EDIT实际上解决了这个问题。



  [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 
 $ b $ 76.00 +78.000000 * i 69.000000 + -57.000000 * i 93.000000 + -11.000000 * i 76.000000 + -78.000000 * i 67.000000 + 0.000000 * i 
  




解决方案

在每次调用 rand 之前，请勿调用 srand 。在程序启动时调用一次。

Its a small code to generate a random hermitian matrix hermitian matrix.

I have called srand() before every call to rand(). but still no randomness in the output.

I have used c99's complex datatype feature to create a hermitian matrix. I'm not sure where i'm wrong :(

#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;
}

sample output

[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    

EDIT calling srand in main() actually solved the problem. Thank you guys.

[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    

解决方案

Don't call srand before every call to rand. Call it once when your program starts.

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