求助,请问如何获取正态分布的随机数 rand()产生的好像是平均分布的随机数,我想获取正态分布的随机数,应该怎么获取呢? 解决方案 » 免费领取超大流量手机卡,每月29元包185G流量+100分钟通话, 中国电信官方发货 参考着转换成sql处理。Box 和 Muller 在 1958 年给出了由均匀分布的随机变量生成正态分布的随机变量的算法。设 U1, U2 是区间 (0, 1) 上均匀分布的随机变量,且相互独立。令X1 = sqrt(-2*log(U1)) * cos(2*PI*U2);X2 = sqrt(-2*log(U1)) * sin(2*PI*U2); 那么 X1, X2 服从 N(0,1) 分布,且相互独立。等于说我们用两个独立的 U(0,1) 随机数得到了两个独立的 N(0,1)随机数。程序如下:double Normal(double x,double miu,double sigma) //概率密度函数 { return 1.0/sqrt(2*PI*sigma) * exp(-1*(x-miu)*(x-miu)/(2*sigma*sigma)); } double NormalRandom(double miu, double sigma,double min,double max)//产生正态分布随机数 { double x; double dScope; double y; do { x = AverageRandom(min,max); y = Normal(dResult, miu, sigma); dScope = AverageRandom(0, Normal(miu,miu,sigma)); }while( dScope > y); return x; }参数说明:double miu:μ,正态函数的数学期望 double sigma:σ,正态函数的均方差 double min,double max,表明产生的随机数的范围 Marsaglia 和 Bray 在 1964 年提出了一种改进算法,避免使用三角函数。以下的实现代码用的就是这种改进算法。// C#.net// Gaussian Random Number Generator class// ref. ``Numerical Recipes in C++ 2/e'', p.293 ~ p.294// public class GaussianRNG { int iset; double gset; Random r1, r2; public GaussianRNG() { r1 = new Random(unchecked((int)DateTime.Now.Ticks)); r2 = new Random(~unchecked((int)DateTime.Now.Ticks)); iset = 0; } public double Next() { double fac, rsq, v1, v2; if (iset == 0) { do { v1 = 2.0 * r1.NextDouble() - 1.0; v2 = 2.0 * r2.NextDouble() - 1.0; rsq = v1*v1 + v2*v2; } while (rsq >= 1.0 || rsq == 0.0); fac = Math.Sqrt(-2.0*Math.Log(rsq)/rsq); gset = v1*fac; iset = 1; return v2*fac; } else { iset = 0; return gset; } } } CREATE FUNCTION dbo.NormalRandom(@seed1 float, -- (0,1]均匀分布随机种子1@seed2 float, -- (0,1]均匀分布随机种子2@mean float, -- 均值@sigma float, -- 标准差@minv float = NULL, -- 最小值@maxv float = NULL -- 最大值)RETURNS floatBEGIN IF @seed1 = 0 OR @seed2 = 0 RETURN 0 DECLARE @random float SET @random = @mean + @sigma * (SQRT(-2 * LOG(@seed1)) * COS(2 * PI() * @seed2)) IF @random < @minv SET @random = @minv IF @random > @maxv SET @random = @maxv RETURN @randomENDGO--单独生成测试SELECT dbo.NormalRandom(RAND(),RAND(),0,1,DEFAULT,DEFAULT) --标准正态分布SELECT CAST(dbo.NormalRandom(RAND(),RAND(),70,20,0,100) AS int) --满分100、平均分70、标准差20的成绩SELECT CAST(dbo.NormalRandom(RAND(),RAND(),100,15,0,DEFAULT) AS int) --IQ分数--批量生成测试DROP TABLE #tempSELECT uniform = ABS(CHECKSUM(NEWID())) % 100 + 1, --1-100均匀分布 normal1 = CAST(dbo.NormalRandom( --1-100正态分布:均值50,标准差20 1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000, 1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000, 50,20,0,100) AS int), normal2 = CAST(dbo.NormalRandom( --1-100正态分布:均值50,标准差10 1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000, 1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000, 50,10,0,100) AS int), normal3 = CAST(dbo.NormalRandom( --1-100正态分布:均值70,标准差10 1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000, 1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000, 70,10,0,100) AS int)INTO #tempFROM dbo.NumsWHERE n BETWEEN 1 AND 100000--查看批量生成的随机数分布情况SELECT i = i.n, uniform = ISNULL(u.cnt,0), normal1 = ISNULL(n1.cnt,0), normal2 = ISNULL(n2.cnt,0), normal3 = ISNULL(n3.cnt,0)FROM (SELECT n FROM dbo.Nums WHERE n BETWEEN 1 AND 100) iLEFT JOIN ( SELECT uniform, cnt = COUNT(*) FROM #temp GROUP BY uniform) uON i.n = u.uniformLEFT JOIN ( SELECT normal1, cnt = COUNT(*) FROM #temp GROUP BY normal1) n1ON i.n = n1.normal1LEFT JOIN ( SELECT normal2, cnt = COUNT(*) FROM #temp GROUP BY normal2) n2ON i.n = n2.normal2LEFT JOIN ( SELECT normal3, cnt = COUNT(*) FROM #temp GROUP BY normal3) n3ON i.n = n3.normal3ORDER BY i把上面最后一个查询的数据放入Excel并生成图表: 帮忙转sql2005数据库文件到sql2000。分全给你 怎么设置表中记录条数? jsp下存储过程的使用问题 【求看】左联合的SQL语句如何写? 这样的情况如何进行统计汇总! 这个查询怎么做?简单,立刻给分!! 关于mssql 全文索引查询 关于产生字符串的问题 关于oracle请各位大侠帮帮忙!简单问题! 如何修改、删除文件名 sql2005 如何导出为mysql ? 大大帮忙写下这个数量分配的sql
Box 和 Muller 在 1958 年给出了由均匀分布的随机变量生成正态分布的随机变量的算法。设 U1, U2 是区间 (0, 1) 上均匀分布的随机变量,且相互独立。令X1 = sqrt(-2*log(U1)) * cos(2*PI*U2);
X2 = sqrt(-2*log(U1)) * sin(2*PI*U2); 那么 X1, X2 服从 N(0,1) 分布,且相互独立。等于说我们用两个独立的 U(0,1) 随机数得到了两个独立的 N(0,1)随机数。程序如下:double Normal(double x,double miu,double sigma) //概率密度函数 { return 1.0/sqrt(2*PI*sigma) * exp(-1*(x-miu)*(x-miu)/(2*sigma*sigma)); } double NormalRandom(double miu,
double sigma,double min,double max)//产生正态分布随机数 { double x; double dScope; double y; do { x = AverageRandom(min,max); y = Normal(dResult, miu, sigma); dScope = AverageRandom(0, Normal(miu,miu,sigma)); }while( dScope > y); return x; }
参数说明:double miu:μ,正态函数的数学期望
double sigma:σ,正态函数的均方差
double min,double max,表明产生的随机数的范围 Marsaglia 和 Bray 在 1964 年提出了一种改进算法,避免使用三角函数。以下的实现代码用的就是这种改进算法。
// C#.net
// Gaussian Random Number Generator class
// ref. ``Numerical Recipes in C++ 2/e'', p.293 ~ p.294
//
public class GaussianRNG
{
int iset;
double gset;
Random r1, r2;
public GaussianRNG()
{
r1 = new Random(unchecked((int)DateTime.Now.Ticks));
r2 = new Random(~unchecked((int)DateTime.Now.Ticks));
iset = 0;
}
public double Next()
{
double fac, rsq, v1, v2;
if (iset == 0) {
do {
v1 = 2.0 * r1.NextDouble() - 1.0;
v2 = 2.0 * r2.NextDouble() - 1.0;
rsq = v1*v1 + v2*v2;
} while (rsq >= 1.0 || rsq == 0.0);
fac = Math.Sqrt(-2.0*Math.Log(rsq)/rsq);
gset = v1*fac;
iset = 1;
return v2*fac;
} else {
iset = 0;
return gset;
}
}
}
CREATE FUNCTION dbo.NormalRandom(
@seed1 float, -- (0,1]均匀分布随机种子1
@seed2 float, -- (0,1]均匀分布随机种子2
@mean float, -- 均值
@sigma float, -- 标准差
@minv float = NULL, -- 最小值
@maxv float = NULL -- 最大值
)
RETURNS float
BEGIN
IF @seed1 = 0 OR @seed2 = 0 RETURN 0
DECLARE @random float
SET @random = @mean + @sigma * (SQRT(-2 * LOG(@seed1)) * COS(2 * PI() * @seed2))
IF @random < @minv SET @random = @minv
IF @random > @maxv SET @random = @maxv
RETURN @random
END
GO--单独生成测试
SELECT dbo.NormalRandom(RAND(),RAND(),0,1,DEFAULT,DEFAULT) --标准正态分布
SELECT CAST(dbo.NormalRandom(RAND(),RAND(),70,20,0,100) AS int) --满分100、平均分70、标准差20的成绩
SELECT CAST(dbo.NormalRandom(RAND(),RAND(),100,15,0,DEFAULT) AS int) --IQ分数--批量生成测试
DROP TABLE #temp
SELECT
uniform = ABS(CHECKSUM(NEWID())) % 100 + 1, --1-100均匀分布
normal1 = CAST(dbo.NormalRandom( --1-100正态分布:均值50,标准差20
1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000,
1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000,
50,20,0,100) AS int),
normal2 = CAST(dbo.NormalRandom( --1-100正态分布:均值50,标准差10
1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000,
1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000,
50,10,0,100) AS int),
normal3 = CAST(dbo.NormalRandom( --1-100正态分布:均值70,标准差10
1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000,
1.0 * ABS(CHECKSUM(NEWID())) % 10000 / 10000,
70,10,0,100) AS int)
INTO #temp
FROM dbo.Nums
WHERE n BETWEEN 1 AND 100000--查看批量生成的随机数分布情况
SELECT i = i.n,
uniform = ISNULL(u.cnt,0),
normal1 = ISNULL(n1.cnt,0),
normal2 = ISNULL(n2.cnt,0),
normal3 = ISNULL(n3.cnt,0)
FROM (SELECT n FROM dbo.Nums WHERE n BETWEEN 1 AND 100) i
LEFT JOIN (
SELECT uniform, cnt = COUNT(*)
FROM #temp
GROUP BY uniform
) u
ON i.n = u.uniform
LEFT JOIN (
SELECT normal1, cnt = COUNT(*)
FROM #temp
GROUP BY normal1
) n1
ON i.n = n1.normal1
LEFT JOIN (
SELECT normal2, cnt = COUNT(*)
FROM #temp
GROUP BY normal2
) n2
ON i.n = n2.normal2
LEFT JOIN (
SELECT normal3, cnt = COUNT(*)
FROM #temp
GROUP BY normal3
) n3
ON i.n = n3.normal3
ORDER BY i把上面最后一个查询的数据放入Excel并生成图表: