Fast Fourier transform: Difference between revisions
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0.000e+00+0.000e+00j,
1.000e+00+2.414e+00j>)</pre>
=={{header|VBA}}==
{{works with|VBA}}
Written and tested in Microsoft Visual Basic for Applications 7.1 under Office 365 Excel; but is probably useable under any recent version of VBA.
<syntaxhighlight lang="vba">Option Base 0
Private Type Complex
re As Double
im As Double
End Type
Private Function cmul(c1 As Complex, c2 As Complex) As Complex
Dim ret As Complex
ret.re = c1.re * c2.re - c1.im * c2.im
ret.im = c1.re * c2.im + c1.im * c2.re
cmul = ret
End Function
Public Sub FFT(buf() As Complex, out() As Complex, begin As Integer, step As Integer, N As Integer)
Dim i As Integer, t As Complex, c As Complex, v As Complex
If step < N Then
FFT out, buf, begin, 2 * step, N
FFT out, buf, begin + step, 2 * step, N
i = 0
While i < N
t.re = Cos(-WorksheetFunction.Pi() * i / N)
t.im = Sin(-WorksheetFunction.Pi() * i / N)
c = cmul(t, out(begin + i + step))
buf(begin + (i \ 2)).re = out(begin + i).re + c.re
buf(begin + (i \ 2)).im = out(begin + i).im + c.im
buf(begin + ((i + N) \ 2)).re = out(begin + i).re - c.re
buf(begin + ((i + N) \ 2)).im = out(begin + i).im - c.im
i = i + 2 * step
Wend
End If
End Sub
' --- test routines:
Private Sub show(r As Long, txt As String, buf() As Complex)
Dim i As Integer
r = r + 1
Cells(r, 1) = txt
For i = LBound(buf) To UBound(buf)
r = r + 1
Cells(r, 1) = buf(i).re: Cells(r, 2) = buf(i).im
Next
End Sub
Sub testFFT()
Dim buf(7) As Complex, out(7) As Complex
Dim r As Long, i As Integer
buf(0).re = 1: buf(1).re = 1: buf(2).re = 1: buf(3).re = 1
r = 0
show r, "Input (real, imag):", buf
FFT out, buf, 0, 1, 8
r = r + 1
show r, "Output (real, imag):", out
End Sub
</syntaxhighlight>
{{out}}
<pre>Input (real, imag):
1 0
1 0
1 0
1 0
0 0
0 0
0 0
0 0
Output (real, imag):
4 0
1 -2,414213562
0 0
1 -0,414213562
0 0
1 0,414213562
0 0
1 2,414213562</pre>
=={{header|Vlang}}==
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