关于一个随机数的问题

[dqdx_zch]

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <vector>
#include "time.h"
using namespace std;

const int N = 50;

int RangedRandDemo( int range_min, int range_max )
{	
	srand( (unsigned)time( NULL ) );
	int u = (double)rand() / (RAND_MAX + 1) * (range_max - range_min) + range_min;
	return u;
}

int _tmain(int argc, _TCHAR* argv[])
{

	vector< vector<double> > r(N);
	char *names[] = {"RandOD1.txt", "RandOD2.txt", "RandOD3.txt", "RandOD4.txt", "RandOD5.txt",
					 "RandOD6.txt", "RandOD7.txt", "RandOD8.txt", "RandOD9.txt", "RandOD10.txt"};

	ifstream infile_R;
	ofstream outfile;

	infile_R.open("bcOD.txt");
	for (size_t i = 0; i < N; ++i)
	{
		for (size_t j = 0; j < N; ++j)
		{
			double num;
			infile_R >> num;
			r[i].push_back(num);
		}
	}

	infile_R.close();
	
	
	double temp[N][N] = {0};
	for (int ix = 0; ix < 10; ++ix)
	{
		srand( (unsigned)time( NULL ) );
		for (int i = 0; i < N; ++i)
		{
			for (int j = 0; j < N; ++j)
			{
				temp[i][j] = r[i][j] + ( RangedRandDemo(1, 100) );
			}
		}
		outfile.open(names[ix]);
		for (size_t i = 0; i < N; ++i)
		{
			for (size_t j = 0; j < N; ++j)
			{
				outfile << temp[i][j] << "       ";
			}
			outfile << endl;
		}
		outfile.close();
		outfile.clear();
	}

	return 0;
}

我这个程序是想对r[i][j]矩阵，用伪随机数进行10次扰动，产生10个扰动的矩阵，但是为什么10个矩阵都是一样的呢？
达人教教啊！

[lingyin55]

srand( (unsigned)time( NULL ) );////放到这里看看
double temp[N][N] = {0};
for (int ix = 0; ix < 10; ++ix)
{

[mengde007]

因为随机种子每次都要产生才能有效果；

[strive0]

scrand(time(0));
试试，随机种子不一样就行了吧应该。。。

[liliangbao]

[Quote=引用 1 楼 lingyin55 的回复:]
srand( (unsigned)time( NULL ) );////放到这里看看
double temp[N][N] = {0};
for (int ix = 0; ix < 10; ++ix)
{
[/Quote]
Up~

[koulongfei]

学习....................

[deerwin1986]

加种子。。。

[aaaa3105563]

帮顶··

[猫已经找不回了]

srand( (unsigned)time( NULL ) );


只需要初始化一次种子，明白不。

[xiaocha]

[Quote=引用 1 楼 lingyin55 的回复:]
srand( (unsigned)time( NULL ) );////放到这里看看
double temp[N][N] = {0};
for (int ix = 0; ix < 10; ++ix)
{
[/Quote]

因为代码执行很快，多次srand( (unsigned)time( NULL ) );时，
time(NULL)都一样，使得种子相同，从而产生的随即数相同，造成错误

[liliangbao]

[Quote=引用 9 楼 xiaocha 的回复:]
引用 1 楼 lingyin55 的回复:
srand( (unsigned)time( NULL ) );////放到这里看看
double temp[N][N] = {0};
for (int ix = 0; ix < 10; ++ix)
{


因为代码执行很快，多次srand( (unsigned)time( NULL ) );时，
time(NULL)都一样，使得种子相同，从而产生的随即数相同，造成错误
[/Quote]
晕，真的假的~
你测试了吗？