使用Excel的VBA进行快速傅里叶变换

时间：2016-04-11 14:55:22

标签： excel algorithm excel-vba signal-processing fft vba

我正在尝试在MS的Excel VBA中实现快速傅里叶变换（Radix-2）。我正在使用的代码从工作表中的范围中提取数据，进行计算，然后将结果转储到相邻列中。我遇到的问题是：1）知道如何处理生成的X [k]数组，以及2）将这些结果与Excel内置的FFT（它们目前不匹配）的结果相匹配。代码如下所示。在此先感谢您的帮助。 

Sub Enforce_DecimationInTime()

On Error GoTo ERROR_HANDLING
Dim SubName As String
SubName = "Enforce_DecimationInTime()"

Dim WS As Worksheet
Dim n As Long, v As Long, LR As Long, x As Long

Set WS = Worksheets("FFT")
LR = WS.Range("A" & Rows.Count).End(xlUp).Row
n = LR - 1
Do Until 2 ^ x <= n And 2 ^ (x + 1) > n     'locates largest power of 2 from size of input array
    x = x + 1
Loop
n = n - (n - 2 ^ x) 'calculates n using the largest power of 2
If n + 1 <> WS.Range("A" & Rows.Count).End(xlUp).Row Then
    WS.Range("A" & 2 ^ x + 2 & ":A" & LR).Delete xlUp   'deletes extra input data
End If
v = WorksheetFunction.Log(n, 2)     'calculates number of decimations necessary

Application.ScreenUpdating = False
For x = 1 To v
    Call Called_Core.DecimationInTime(WS, n, 2 ^ x, x)  'calls decimation in time subroutine
Next x
Application.ScreenUpdating = True

Exit Sub
ERROR_HANDLING:
    MsgBox "Error encountered in " & SubName & ": exiting subroutine." _
    & vbNewLine _
    & vbNewLine & "Error description: " & Err.Description _
    & vbNewLine & "Error number: " & Err.Number, vbCritical, Title:="Error!"
    End

End Sub

上面的子程序通过For / Next循环调用下面的子程序来计算“v”。

Sub DecimationInTime(WS As Worksheet, n As Long, Factor As Integer, x As Long)

On Error GoTo ERROR_HANDLING
Dim SubName As String
SubName = "DecimationInTime()"

Dim f_1() As Single, f_2() As Single
Dim i As Long, m As Long, k As Long
Dim TFactor_N1 As String, TFactor_N2 As String, X_k() As String
Dim G_1() As Variant, G_2() As Variant

ReDim f_1(0 To n / Factor - 1) As Single
ReDim f_2(0 To n / Factor - 1) As Single
ReDim G_1(0 To n / 1 - 1) As Variant
ReDim G_2(0 To n / 1 - 1) As Variant
ReDim X_k(0 To n - 1) As String

TFactor_N1 = WorksheetFunction.Complex(0, -2 * WorksheetFunction.Pi / (n / 1))  'twiddle factor for N
TFactor_N2 = WorksheetFunction.Complex(0, -2 * WorksheetFunction.Pi / (n / 2))  'twiddle factor for N/2

For i = 0 To n / Factor - 1
    f_1(i) = WS.Range("A" & 2 * i + 2).Value    'assign input data
    f_2(i) = WS.Range("A" & 2 * i + 3).Value    'assign input data
Next i

WS.Cells(1, 1 + x).Value = "X[" & x & "]"   'labels X[k] column with k number
For k = 0 To n / 2 - 1
    For m = 0 To n / Factor - 1
        G_1(m) = WorksheetFunction.ImProduct(WorksheetFunction.ImPower(TFactor_N2, k * m), WorksheetFunction.Complex(f_1(m), 0))    'defines G_1[m]
        G_2(m) = WorksheetFunction.ImProduct(WorksheetFunction.ImPower(TFactor_N2, k * m), WorksheetFunction.Complex(f_2(m), 0))    'defines G_2[m]
    Next m
    X_k(k) = WorksheetFunction.ImSum(WorksheetFunction.ImSum(G_1), WorksheetFunction.ImProduct(WorksheetFunction.ImSum(G_2), WorksheetFunction.ImPower(TFactor_N1, k)))  'defines X[k] for k
    If k <= n / 2 Then X_k(k + n / 2) = WorksheetFunction.ImSum(WorksheetFunction.ImSum(G_1), WorksheetFunction.ImProduct(WorksheetFunction.ImSum(G_2), WorksheetFunction.ImPower(TFactor_N1, k), WorksheetFunction.Complex(-1, 0)))  'defines X[k] for k + n/2
    WS.Cells(k + 2, 1 + x).Value = X_k(k)
    WS.Cells(k + 2 + n / 2, 1 + x).Value = X_k(k + n / 2)
Next k

Exit Sub
ERROR_HANDLING:
    MsgBox "Error encountered in " & SubName & ": exiting subroutine." _
    & vbNewLine _
    & vbNewLine & "Error description: " & Err.Description _
    & vbNewLine & "Error number: " & Err.Number, vbCritical, Title:="Error!"
    End

End Sub

1 个答案:

答案 0 :(得分：2)

我回过头来确定我的问题是我为旋转因子TFactor_N1和TFactor_N2分配了错误的值。修复此问题并调整显示哪些值后，我能够获得与Excel内置FFT相同的结果。固定代码如下所示。

Sub Enforce_DecimationInTime()

On Error GoTo ERROR_HANDLING
Dim SubName As String
SubName = "Enforce_DecimationInTime()"

Dim WS As Worksheet
Dim n As Long, v As Long, LR As Long, x As Long
Dim TFactor_N1 As String, TFactor_N2 As String

Set WS = Worksheets("FFT")
LR = WS.Range("A" & Rows.Count).End(xlUp).Row
n = LR - 1
Do Until 2 ^ x <= n And 2 ^ (x + 1) > n                                                                     'locates largest power of 2 from size of input array
    x = x + 1
Loop
n = n - (n - 2 ^ x)                                                                                         'calculates n using the largest power of 2
If n + 1 <> WS.Range("A" & Rows.Count).End(xlUp).Row Then
    WS.Range("A" & 2 ^ x + 2 & ":A" & LR).Delete xlUp                                                       'deletes extra input data
End If
v = WorksheetFunction.Log(n, 2)                                                                             'calculates number of decimations necessary

TFactor_N1 = WorksheetFunction.ImExp(WorksheetFunction.Complex(0, -2 * WorksheetFunction.Pi / (n / 1)))     'twiddle factor for N
TFactor_N2 = WorksheetFunction.ImExp(WorksheetFunction.Complex(0, -2 * WorksheetFunction.Pi / (n / 2)))     'twiddle factor for N/2

Application.ScreenUpdating = False
For x = 1 To v
    Call Called_Core.DecimationInTime(WS, n, 2 ^ x, x, TFactor_N1, TFactor_N2)                              'calls decimation in time subroutine
Next x
Application.ScreenUpdating = True

Exit Sub
ERROR_HANDLING:
    MsgBox "Error encountered in " & SubName & ": exiting subroutine." _
    & vbNewLine _
    & vbNewLine & "Error description: " & Err.Description _
    & vbNewLine & "Error number: " & Err.Number, vbCritical, Title:="Error!"
    End

End Sub


Sub DecimationInTime(WS As Worksheet, n As Long, Factor As Integer, x As Long, TFactor_N1 As String, TFactor_N2 As String)

On Error GoTo ERROR_HANDLING
Dim SubName As String
SubName = "DecimationInTime()"

Dim f_1() As String, f_2() As String
Dim i As Long, m As Long, k As Long
Dim X_k() As String
Dim G_1() As Variant, G_2() As Variant

ReDim f_1(0 To n / Factor - 1) As String
ReDim f_2(0 To n / Factor - 1) As String
ReDim G_1(0 To n / 1 - 1) As Variant
ReDim G_2(0 To n / 1 - 1) As Variant
ReDim X_k(0 To n - 1) As String

For i = 0 To n / Factor - 1
    f_1(i) = WS.Cells(2 * i + 2, 1).Value                                                                   'assign input data
    f_2(i) = WS.Cells(2 * i + 3, 1).Value                                                                   'assign input data
Next i
For k = 0 To n / 2 - 1
    For m = 0 To n / Factor - 1                                                                             'defines G_1[m] and G_2[m]
        G_1(m) = WorksheetFunction.ImProduct(WorksheetFunction.ImPower(TFactor_N2, k * m), f_1(m))
        G_2(m) = WorksheetFunction.ImProduct(WorksheetFunction.ImPower(TFactor_N2, k * m), f_2(m))
    Next m                                                                                                  'defines X[k] for k and k + n/2
    X_k(k) = WorksheetFunction.ImSum(WorksheetFunction.ImSum(G_1), WorksheetFunction.ImProduct(WorksheetFunction.ImSum(G_2), WorksheetFunction.ImPower(TFactor_N1, k)))
    If k <= n / 2 Then X_k(k + n / 2) = WorksheetFunction.ImSub(WorksheetFunction.ImSum(G_1), WorksheetFunction.ImProduct(WorksheetFunction.ImSum(G_2), WorksheetFunction.ImPower(TFactor_N1, k)))
    If x = 1 Then
        WS.Cells(k + 2, 1 + x).Value = X_k(k)
        WS.Cells(k + 2 + n / 2, 1 + x).Value = X_k(k + n / 2)
    End If
Next k

Exit Sub
ERROR_HANDLING:
    MsgBox "Error encountered in " & SubName & ": exiting subroutine." _
    & vbNewLine _
    & vbNewLine & "Error description: " & Err.Description _
    & vbNewLine & "Error number: " & Err.Number, vbCritical, Title:="Error!"
    End

End Sub
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