- Make a function to calculate
summation (a.k.a. Sigma, Σ)
- Change the calculation method from loop to Faulhaber's Formula (make faster)
- Support operations for k ~ k^4
Option Explicit
Function Sigma4(p As Integer, a As Integer, n As Integer) As Integer
On Error GoTo ErrorHandler1
If a > n Then
Err.Raise 380 'Error Code 380 : Invalid property value.
End If
On Error GoTo ErrorHandler2
Dim sum As Integer
If p = 1 Then
sum = n * (n + 1) / 2 - (a - 1) * a / 2
ElseIf p = 2 Then
sum = n * (n + 1) * (2 * n + 1) / 6 - (a - 1) * a * (2 * (a - 1) + 1) / 6
ElseIf p = 3 Then
sum = (n * (n + 1) / 2) ^ 2 - ((a - 1) * a / 2) ^ 2
ElseIf p = 4 Then
sum = n * (n + 1) * (2 * n + 1) * (3 * n ^ 2 + 3 * n - 1) / 30 - (a - 1) * a * (2 * (a - 1) + 1) * (3 * (a - 1) ^ 2 + 3 * (a - 1) - 1) / 30
Else 'When p > 4
Err.Raise 380
End If
Sigma4 = sum
Exit Function
ErrorHandler1:
MsgBox "An error occurs : Starting number a is greater than final number n."
Exit Function
ErrorHandler2:
MsgBox "An error occurs : Sigma4() supports only power numbers under 5."
End Function
- Add Error Handler
- How about naming labels such like
try ~ catch ~ finally?
Option Explicit
Function Sigma3(k As Integer, n As Integer) As Integer
On Error GoTo ErrorHandler
If k > n Then
Err.Raise 380 'Error Code 380 : Invalid property value.
End If
Dim i As Integer, Sum As Integer
For i = k To n 'including both of k and n
Sum = Sum + i
Next i
Sigma3 = Sum
Exit Function
ErrorHandler:
MsgBox "Error occurs : Starting number k is greater than final number n."
End Function
- Add a parameter of k that indicates a starting point
- Need to add codes for handling errors.
Option Explicit
Function Sigma2(k As Integer, n As Integer) As Integer
Dim i As Integer, Sum As Integer
For i = k To n
Sum = Sum + i
Next i
Sigma2 = Sum
End Function
- Define all the variables as
integer
Option Explicit
Function Sigma(n As Integer) As Integer
Dim i As Integer, Sum As Integer
For i = 1 To n
Sum = Sum + i
Next i
Sigma = Sum
End Function
