Plot A Fourier Transform of Any Curve Using Vb.Net

Below is the code for generation of Fourier Series
of any Function.
The program uses N point DFT, of sampled version of analog signal function entered in the text box.


This is code for Fourier.vb

Imports System.Math Imports MSScriptControl Public Class Fourier Private Sub Fourier_Load(ByVal sender As System.Object,_ ByVal e As System.EventArgs) Handles MyBase.Load CurvePic.BackColor = Color.White End Sub Private Sub DrawBtn_Click(ByVal sender As System.Object,_ ByVal e As System.EventArgs) Handles DrawBtn.Click Dim CurveScript As New MSScriptControl.ScriptControl CurveScript.Language = "VBscript" Dim CurveGraph As Graphics Dim x, y As Double Dim ox, oy As Integer Dim posx, posy As Long Dim curve(,) As Double Dim xacc As Double Dim scl As Double Dim count As Long = 0 ox = CurvePic.Width / 2 oy = CurvePic.Height / 2 xacc = 0.01 scl = 10 CurveGraph = Graphics.FromHwnd(CurvePic().Handle) CurveGraph.Clear(Color.White) ReDim curve(CurvePic.Width / (xacc * scl), 2) For x = -CurvePic.Width / (2 * scl) To _ CurvePic.Width / (2 * scl) Step xacc CurveScript.ExecuteStatement("x=" & x) CurveScript.ExecuteStatement("pi=" & PI) CurveScript.ExecuteStatement("u=" & u(x)) Try y = CurveScript.Eval(FunctionTxt.Text) 'Me.Text = CStr(y) Catch e1 As OverflowException y = 0 Catch e2 As Exception MsgBox(e2.ToString) Exit For End Try curve(count, 0) = x curve(count, 1) = y posx = ox + curve(count, 0) * scl posy = oy - curve(count, 1) * scl Try CurveGraph.DrawRectangle(pen:=Pens.Blue, _ height:=1, width:=1, x:=posx, y:=posy) Catch e1 As OverflowException posx = CurvePic.Width posy = CurvePic.Height End Try count += 1 Next Dim N As Long Dim k As Double Dim nf As Double Dim Reyf As Double Dim imyf As Double Dim ampyf As Double Dim angyf As Double Dim fsclx, fscly As Double Dim famp As Long Dim fang As Long N = count count = 0 fsclx = CurvePic.Width / N fscly = CurvePic.Height / (2 * N) Dim dReyf As Double = 0 Dim dImyf As Double = 0 Dim kr As Double Dim posref, posimf As Long For k = -(N - 1) / 2 To (N - 1) / 2 Step 1 dReyf = 0 dImyf = 0 For nf = 0 To N - 1 Step 1 Reyf = dReyf + curve(nf, 1) * Cos(2 * PI * nf * k / N) imyf = dImyf - curve(nf, 1) * Sin(2 * PI * nf * k / N) dReyf = Reyf dImyf = imyf Next ampyf = (Reyf ^ 2 + imyf ^ 2) ^ 0.5 angyf = Atan(imyf / Reyf) Try famp = oy - ampyf * fscly fang = oy - angyf * (CurvePic.Height / 6) Catch e1 As Exception MsgBox(e1.ToString) Exit For End Try kr = N / 2 + k posref = ox + Reyf * CurvePic.Width / N posimf = oy - imyf * CurvePic.Height / N Try CurveGraph.DrawRectangle(pen:=Pens.Red,_ height:=1, width:=1, x:=CInt(kr * fsclx), y:=famp) CurveGraph.DrawRectangle(pen:=Pens.DarkKhaki,_ height:=1, width:=1, x:=CInt(kr * fsclx), y:=fang) CurveGraph.DrawRectangle(pen:=Pens.Black, _ width:=1, height:=1, x:=posref, y:=posimf) 'Me.Text = CStr(N) + "," + CStr(famp) + "," +_ CStr(fang) + "," + CStr(k) Catch e1 As OverflowException famp = 0 Catch e2 As Exception MsgBox(e2.ToString) Exit For End Try Next End Sub Public Function u(ByVal t As Double) As Double If t < 0 Then Return 0 Else Return 1 End If End Function End Class

now the code for Fourier.Designer.vb

<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _ Partial Class Fourier Inherits System.Windows.Forms.Form 'Form overrides dispose to clean up the component list. <System.Diagnostics.DebuggerNonUserCode()> _ Protected Overrides Sub Dispose(ByVal disposing As Boolean) Try If disposing AndAlso components IsNot Nothing Then components.Dispose() End If Finally MyBase.Dispose(disposing) End Try End Sub 'Required by the Windows Form Designer Private components As System.ComponentModel.IContainer 'NOTE: The following procedure is required by the Windows Form Designer 'It can be modified using the Windows Form Designer. 'Do not modify it using the code editor. <System.Diagnostics.DebuggerStepThrough()> _ Private Sub InitializeComponent() Me.CurvePic = New System.Windows.Forms.PictureBox() Me.DrawBtn = New System.Windows.Forms.Button() Me.FunctionTxt = New System.Windows.Forms.TextBox() Me.StatusTxt = New System.Windows.Forms.TextBox() CType(Me.CurvePic, System.ComponentModel.ISupportInitialize)_ .BeginInit() Me.SuspendLayout() ' 'CurvePic ' Me.CurvePic.Location = New System.Drawing.Point(12, 12) Me.CurvePic.Name = "CurvePic" Me.CurvePic.Size = New System.Drawing.Size(768, 413) Me.CurvePic.TabIndex = 0 Me.CurvePic.TabStop = False ' 'DrawBtn ' Me.DrawBtn.Location = New System.Drawing.Point(12, 431) Me.DrawBtn.Name = "DrawBtn" Me.DrawBtn.Size = New System.Drawing.Size(75, 23) Me.DrawBtn.TabIndex = 1 Me.DrawBtn.Text = "Transform" Me.DrawBtn.UseVisualStyleBackColor = True ' 'FunctionTxt ' Me.FunctionTxt.Location = New System.Drawing.Point(93, 434) Me.FunctionTxt.Name = "FunctionTxt" Me.FunctionTxt.Size = New System.Drawing.Size(215, 20) Me.FunctionTxt.TabIndex = 2 Me.FunctionTxt.Text = "10*sin(x)" ' 'StatusTxt ' Me.StatusTxt.Location = New System.Drawing.Point(314, 433) Me.StatusTxt.Name = "StatusTxt" Me.StatusTxt.Size = New System.Drawing.Size(221, 20) Me.StatusTxt.TabIndex = 3 ' 'Fourier ' Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!) Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font Me.ClientSize = New System.Drawing.Size(792, 466) Me.Controls.Add(Me.StatusTxt) Me.Controls.Add(Me.FunctionTxt) Me.Controls.Add(Me.DrawBtn) Me.Controls.Add(Me.CurvePic) Me.Name = "Fourier" Me.Text = "Forier Transform" CType(Me.CurvePic, System.ComponentModel.ISupportInitialize)_ .EndInit() Me.ResumeLayout(False) Me.PerformLayout() End Sub Friend WithEvents CurvePic As System.Windows.Forms.PictureBox Friend WithEvents DrawBtn As System.Windows.Forms.Button Friend WithEvents FunctionTxt As System.Windows.Forms.TextBox Friend WithEvents StatusTxt As System.Windows.Forms.TextBox End Class

Note: if code doesn't work try to remove underscores at the end of various line and then try.

Download Demo executable here.