Public Function ForwardEuler( _
   ByVal s0 As Double, _
   ByVal k As Double, _
   ByVal T As Double, _
   ByVal sigma As Double, _
   ByVal r As Double, _
   ByVal periods As Integer)  '  Use the forward Euler trinomial tree
method to price an option

   DelT = T / periods         '  The size of a time period do that n equal
periods fit
   delX = sigma * Sqr(DelT)   '  The size of the space step if  . . .
   Xmin = -periods * delX     '  The minimum value of x on the
computational grid

   If periods > 200 Then      '  The VBA syntax for the "if" test.  Here
return if you don't
                              '  have memory for that many time steps.
      ForwardEuler = -0.12345 '  return a silly value that hopefully would
be recognized
      Return                  '  stop the program here.
   End If

   Dim f(-200 To 200, 200) As Double  '  The VBA syntax for dimensioning
an array.  Note that the
                                      '  range of the j index is -period
to period and the n index
                                      '  is from 1 to period.  "Double" is
the type.

   For j = -periods To periods        '  The VBA syntax for the start of a
"for" loop.
      x = delX * j                    '  Calculate the final values . . .
      IntVal = x                      '  not the right formula
      If (IntVal < 0) Then
         f(k, periods) = 0            '  and put them in the appropriate
place in the f array
      Else
         f(k, periods) = IntVal
      End If
   Next j                             '  The end of the "for" loop.

   a = 0.3333       ' not the real coefficients.
   b = 0.3333
   c = 0.3333

   For n = periods To 2 Step -1       '  This goes from the end to the
beginning in steps of -1
      For j = -(n - 1) To (n - 1)     '  You can put a loop inside another
loop
         f(j, n - 1) = a * f(j + 1, n) + b * f(j, n) + c * f(j + 1, n)  '
The actual formula
      Next j
   Next n

   ForwardEuler = f(0, 1)      '  You return a value by assigning the
function name the desired value.
                               '  here j = 0 means spot price, n=1 means
start time.

   End Function

Public Function BlackScholesEuropeanPut( _
   ByVal s0 As Double, _
   ByVal k As Double, _
   ByVal T As Double, _
   ByVal sigma As Double, _
   ByVal r As Integer)

   BlackScholesEuropeanPut = Application.WorksheetFunction.NormSDist(s0) '
This is how you access the
                                                                         '
Excel
function
NormSDist
from
VBA.

   End Function