Question

我正在尝试尽可能快地增加数组。将有非常大的阵列，乘以很多次。我有以下代码使用嵌套循环，有没有更快的方法这样做？我有数组a（）和b（），我想使sum（1）= a（1）* b（1）+ a（1）* b（2）+ a（1）* b（3）等。

目前我在Excel VBA中，但我很快就会转换为VBA.NET。这比在excel vba中运行它要快多少？我可以使用.Net中更快的方法吗？

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

除非您的示例过度简化，否则您可以通过总结b()值来删除内部循环，因为

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

相当于

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可以改善现状，因为现代处理器需要花费更长的时间来从内存中读取数值。我也会考虑loop unrolling，但您必须使用高性能计时器进行测试，看看它是否有帮助。

Excel VBA和.NET中最快的乘法数组方式

2 个答案: