2-2-CG-2-r=a・EXP(ｂθ)

この絵の形は、自然界に多くあります。

アンモナイト、カタツムリ、低気圧の雲、等です。

Excel macro aEXP()

      Sub aEXP()

      Dim x(1001) As Double

      Dim y(1001) As Double

      Set RngStart = Worksheets("Sheet1").Range("B40")

      xs = RngStart.Left

      ys = RngStart.Top

      Set RngEnd = Worksheets("Sheet1").Range("D4")

      ye = RngEnd.Top

      xe = xs + (ys - ye)

      pai = 3.14159265

      a = 1000#

      b = 0.1

      dp = 13# * pai / 1000#

      For i = 1 To 1000

      theta = i * dp

      r = a * Exp(b * theta)

      x(i) = r * Cos(theta)

      y(i) = r * Sin(theta)

      Next i

      xmax = -100000#

      ymax = -100000#

      xmin = 100000#

      ymin = 100000#

      For i = 1 To 1000

      If (x(i) > xmax) Then

      xmax = x(i)

      Else

      End If

      If (x(i) < xmin) Then

      xmin = x(i)

      Else

      End If

      If (y(i) > ymax) Then

      ymax = y(i)

      Else

      End If

      If (y(i) < ymin) Then

      ymin = y(i)

      Else

      End If

      Next i

      If (xmax > ymax) Then

      ymax = xmax

      Else

      xmax = ymax

      End If

      If (xmin < ymin) Then

      ymin = xmin

      Else

      xmin = ymin

      End If

      dx = (xe - xs) / (xmax - xmin)

      dy = (ye - ys) / (ymax - ymin)

      xg = (xe - xs) * (-xmin / (xmax - xmin)) + xs

      yg = (ye - ys) * (-ymin / (ymax - ymin)) + ys

      For i = 1 To 999

      x1 = x(i) * dx + xg

      y1 = y(i) * dy + yg

      x2 = x(i + 1) * dx + xg

      y2 = y(i + 1) * dy + yg

      ActiveSheet.Shapes.AddLine x1, y1, x2, y2

      Next i

      End Sub