真正意义上的随机数（或者随机事件）在某次产生过程中是按照实验过程中表现的分布概率随机产生的，其结果是不可预测的，是不可见的。而计算机中的随机函数是按照一定算法模拟产生的，其结果是确定的，是可见的。我们可以这样认为这个可预见的结果其出现的概率是100%。所以用计算机随机函数所产生的“随机数”并不随机，是伪随机数。伪随机数的作用在开发中的使用非常常见，因此.NET在System命名空间，提供了一个简单的Random随机数生成类型。但这个类型并不能满足所有的需求，本节开始就将陆续介绍Math.NET中有关随机数的扩展以及其他伪随机生成算法编写的随机数生成器。
Rondom扩展及随机数相关的类都在Math.NET的MathNet.Numerics.Random命名空间，今天要介绍的 RandomExtensions 类是 扩展Random的静态方法类，可以直接在System.Random的对象上使用，相关功能介绍：
1.可以直接返回填充0-1随机数据的数组，如NextDoubles方法；
2.可以返回一个无限长度的IEnumerable接口对象，一直迭代返回double类型的随机数，是NextDoubleSequence方法；
3.类似的还可以返回其他类型的随机数据数组，如NextBytes，NextInt32s等；
4.还可以单独返回Int32类型和Int64类型的随机数，其范围在该类型的所有值域上，如NextFullRangeInt32，NextFullRangeInt64；
5.还可以单独返回Int32类型和Int64类型的随机数，其范围是该类型所有值域上的非负数,如NextInt64;
1 /// <summary>这个类是对System.Random类的扩展，扩展方法可以生成更多类型的伪随机数，而不是仅仅是double和Int32类型</summary>
2 /// <remarks>这个扩展是线程安全的，并且只有在Math.NET提供的随机数发生器或者RandomSource的继承类中被调用</remarks>
3 public static class RandomExtensions
4 {
5 /// <summary>使用(0-1)范围内的均匀随机数填充1个数组</summary>
6 /// <param name="rnd">Random类型的随机数生成器</param>
7 /// <param name="values">要填充随机数的数组</param>
8 /// <remarks>这个扩展是线程安全的，并且只有在Math.NET提供的随机数发生器或者RandomSource的继承类中被调用</remarks>
9 public static void NextDoubles(this System.Random rnd, double[] values)
10 {
11 var rs = rnd as RandomSource;
12 if (rs != null)
13 {
14 rs.NextDoubles(values);
15 return;
16 }
17
18 for (var i = 0; i < values.Length; i++)
19 {
20 values[i] = rnd.NextDouble();
21 }
22 }
23
24 /// <summary>返回一个(0-1)范围内的均匀随机数填充1个数组</summary>
25 /// <param name="rnd">Random类型的随机数生成器</param>
26 /// <param name="count">要返回的数组的长度</param>
27
28 public static double[] NextDoubles(this System.Random rnd, int count)
29 {
30 var values = new double[count];
31 NextDoubles(rnd, values);
32 return values;
33 }
34
35 /// <summary>返回1个无限的0-1均匀分布随机数序列</summary>
36 public static IEnumerable<double> NextDoubleSequence(this System.Random rnd)
37 {
38 var rs = rnd as RandomSource;
39 if (rs != null) return rs.NextDoubleSequence();
40 return NextDoubleSequenceEnumerable(rnd);
41 }
42
43 static IEnumerable<double> NextDoubleSequenceEnumerable(System.Random rnd)
44 {
45 while (true)
46 {
47 yield return rnd.NextDouble();
48 }
49 }
50
51 /// <summary>返回1个均匀分布的byte数组</summary>
52 /// <param name="rnd">Random类型的随机数生成器</param>
53 /// <param name="count">要返回的数组的长度</param>
54 public static byte[] NextBytes(this System.Random rnd, int count)
55 {
56 var values = new byte[count];
57 rnd.NextBytes(values);
58 return values;
59 }
60
61 /// <summary>
62 /// Fills an array with uniform random numbers greater than or equal to 0.0 and less than 1.0.
63 /// </summary>
64 /// <param name="rnd">The random number generator.</param>
65 /// <param name="values">The array to fill with random values.</param>
66 /// <param name="minInclusive">Lower bound, inclusive.</param>
67 /// <param name="maxExclusive">Upper bound, exclusive.</param>
68 public static void NextInt32s(this System.Random rnd, int[] values, int minInclusive, int maxExclusive)
69 {
70 var rs = rnd as RandomSource;
71 if (rs != null)
72 {
73 rs.NextInt32s(values, minInclusive, maxExclusive);
74 return;
75 }
76 for (var i = 0; i < values.Length; i++)
77 {
78 values[i] = rnd.Next(minInclusive, maxExclusive);
79 }
80 }
81
82 /// <summary>
83 /// Returns an infinite sequence of uniform random numbers greater than or equal to 0.0 and less than 1.0.
84 /// </summary>
85 public static IEnumerable<int> NextInt32Sequence(this System.Random rnd, int minInclusive, int maxExclusive)
86 {
87 var rs = rnd as RandomSource;
88 if (rs != null)
89 {
90 return rs.NextInt32Sequence(minInclusive, maxExclusive);
91 }
92 return NextInt32SequenceEnumerable(rnd, minInclusive, maxExclusive);
93 }
94
95 static IEnumerable<int> NextInt32SequenceEnumerable(System.Random rnd, int minInclusive, int maxExclusive)
96 {
97 while (true)
98 {
99 yield return rnd.Next(minInclusive, maxExclusive);
100 }
101 }
102
103 /// <summary>返回Int64类型的非负随机数</summary>
104 /// <param name="rnd">Random类型的随机数生成器</param>
105 /// <returns>
106 /// A 64-bit signed integer greater than or equal to 0, and less than <see cref="Int64.MaxValue"/>; that is,
107 /// the range of return values includes 0 but not <see cref="Int64.MaxValue"/>.
108 /// </returns>
109 /// <seealso cref="NextFullRangeInt64"/>
110 public static long NextInt64(this System.Random rnd)
111 {
112 var buffer = new byte[sizeof (long)];
113
114 rnd.NextBytes(buffer);
115 var candidate = BitConverter.ToInt64(buffer, 0);
116
117 candidate &= long.MaxValue;
118 return (candidate == long.MaxValue) ? rnd.NextInt64() : candidate;
119 }
120
121 /// <summary>
122 /// Returns a random number of the full Int32 range.
123 /// </summary>
124 /// <param name="rnd">The random number generator.</param>
125 /// <returns>
126 /// A 32-bit signed integer of the full range, including 0, negative numbers,
127 /// <see cref="Int32.MaxValue"/> and <see cref="Int32.MinValue"/>.
128 /// </returns>
129 /// <seealso cref="System.Random.Next()"/>
130 public static int NextFullRangeInt32(this System.Random rnd)
131 {
132 var buffer = new byte[sizeof (int)];
133 rnd.NextBytes(buffer);
134 return BitConverter.ToInt32(buffer, 0);
135 }
136
137 /// <summary>
138 /// Returns a random number of the full Int64 range.
139 /// </summary>
140 /// <param name="rnd">The random number generator.</param>
141 /// <returns>
142 /// A 64-bit signed integer of the full range, including 0, negative numbers,
143 /// <see cref="Int64.MaxValue"/> and <see cref="Int64.MinValue"/>.
144 /// </returns>
145 /// <seealso cref="NextInt64"/>
146 public static long NextFullRangeInt64(this System.Random rnd)
147 {
148 var buffer = new byte[sizeof (long)];
149 rnd.NextBytes(buffer);
150 return BitConverter.ToInt64(buffer, 0);
151 }
152
153 /// <summary>
154 /// Returns a nonnegative decimal floating point random number less than 1.0.
155 /// </summary>
156 /// <param name="rnd">The random number generator.</param>
157 /// <returns>
158 /// A decimal floating point number greater than or equal to 0.0, and less than 1.0; that is,
159 /// the range of return values includes 0.0 but not 1.0.
160 /// </returns>
161 public static decimal NextDecimal(this System.Random rnd)
162 {
163 decimal candidate;
164
165 // 50.049 % chance that the number is below 1.0. Try until we have one.
166 // Guarantees that any decimal in the interval can
167 // indeed be reached, with uniform probability.
168 do
169 {
170 candidate = new decimal(
171 rnd.NextFullRangeInt32(),
172 rnd.NextFullRangeInt32(),
173 rnd.NextFullRangeInt32(),
174 false,
175 28);
176 }
177 while (candidate >= 1.0m);
178
179 return candidate;
180 }
181 }
