在 Excel VBA 和 .NET 中乘以数组的最快方法

Question

我正在尝试尽快将数组相乘。会有非常大的数组，成倍增加很多倍。我有下面使用嵌套循环的代码，有没有更快的方法呢？我有数组 a() 和 b()，我想让 sum(1) = a(1)*b(1) + a(1)*b(2) + a(1)*b(3)等等。

目前我在 Excel VBA 中，但我将很快转换为 VBA.NET。这应该比在 excel vba 中运行它快多少？ .Net 中是否有更快的方法可供我使用？

Sub Test()
 ' Just creating the arrays
 Dim a() as Integer, b() as Integer, sum() as Integer, i as Integer, j as Integer
 ReDim a(1 to 3)
 ReDim b(1 to 3)
 ReDim sum(1 to 3)

 For i = 1 to 3 
  a(i) = 2 * i
  b(i) = 3 * i
 Next i

 ' This is my code I am  interested in
 For i = 1 to 3
  For j = 1 to 3
   sum(i) = sum(i) + a(i) * b(j)
  Next j
 Next i

Answer 1

除非您的示例过于简化，否则您可以通过总结您的 b() 值来移除内部循环，因为

a*p + a*q + a*r + ... + a*z

等价于

a * (p+q+r+...+z)

所以：

Sub Test()

    Dim a(), b(), sum(), i As Long, j As Long, tmp, t, n As Long, tmp2
    ReDim a(1 To 20000)
    ReDim b(1 To 50)
    ReDim sum(1 To 20000)

    For i = 1 To 20000
        a(i) = i / 100
    Next i

    tmp2 = 0
    For i = 1 To 50
        b(i) = i / 100
        tmp2 = tmp2 + b(i)
    Next i

    t = Timer
    For n = 1 To 100
        For i = 1 To 20000
            For j = 1 To 50
             sum(i) = sum(i) + a(i) * b(j)
            Next j
        Next i
    Next n
    Debug.Print Timer - t ' ~5.5sec

    ReDim sum(1 To 20000)

    t = Timer
    For n = 1 To 100
        For i = 1 To 20000
            sum(i) = a(i) * tmp2
        Next i
    Next n
    Debug.Print Timer - t ' ~ 0.1 sec

End Sub

Answer 2

这应该更快：

' This is my code I am  interested in
For i = 1 to 3
  ai = a(i)
  sumi = 0#
  For j = 1 to 3
    sumi = sumi + ai * b(j)
  Next j
  sum(i) = sumi
Next i

减少查找数组变量的次数应该会有所改善，因为现代处理器需要更长的时间从内存中读取以乘以值。我也会考虑loop unrolling，但您必须使用高性能计时器进行测试，看看是否有帮助。