deluth said:
Please help me put together a function to calculate
a sum series as follows:
For n = 0 to n=(B3-B1): sum ((A1 + (A3*n)) * A6)
Well, you could write the following UDF. Note that the variable names a1,
a3, etc do not have to match the cell names. I use them just to help you
relate to the above formula. You can call the UDF from Excel with any cells;
for example: =mysum(A1,A3,A6,B1,B3)
However, note that the series sum can be reduced to a single algebraic
formula. So instead of the UDF, you can write:
=A6* (A1*(B3-B1+1) + A3*(B3-B1)*(B3-B1+1)/2)
which can be simplified further to:
=A6 * (B3-B1+1) * (A1+A3*(B3-B1)/2)
UDF....
Option Explicit
Function mysum(a1 As Double, a3 As Double, _
a6 As Double, b1 As Double, b3 As Double) _
As Double
Dim s As Double, n As Double
s = 0
For n = 0 To b3 - b1
s = s + (a1 + (a3 * n)) * a6
Next
mysum = s
End Function
