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# Calculating a series in Excel

How do I calculate a series in Excel? By  series I mean
something like the sum of
[E**1/1!]+[E**2/2!]+......[E**x/x!]
E**x means E to the power X.
0
PaganPig
Asked:
• 2
1 Solution

Commented:
Hi,

You need to use the formula SERIESSUM.

FInd below an extract of the help file

Returns the sum of a power series based on the formula:

Many functions can be approximated by a power series expansion.
If this function is not available, run the Setup program to install the Analysis ToolPak. After you install the Analysis ToolPak, you must enable it by using the Add-Ins command on the Tools menu.

How?

Syntax

SERIESSUM(x,n,m,coefficients)

X   is the input value to the power series.

N   is the initial power to which you want to raise x.

M   is the step by which to increase n for each term in the series.

Coefficients   is a set of coefficients by which each successive power of x is multiplied. The number of values in coefficients determines the number of terms in the power series. For example, if there are three values in coefficients, then there will be three terms in the power series.

Remark

If any argument is nonnumeric, SERIESSUM returns the #VALUE! error value.

Hope this helps

Frazer
0

Author Commented:
Frazer's answer is simply a cut and paste from the Excel help file. I need to know how to apply the formula.

Relating the example I gave, [E**1/1!]+[E**2/2!]+......[E**y/y!], to the help file:
X (the input value to the power series) = E;
N (the initial power to which you want to raise x) = 1;
M (the step by which to increase n for each term in the series) =1

I need to know how to do the following in order to use the formula. How do I
a) specify a value for y - ie, the upper limit for y?
b) define [1/y!] as the coefficient?

0

Commented:
Maybe I don't understand something, but I think, SERIESSUM could not be used in this situation. Why not write user defined function like that:
Function MySeries(e As Double, x As Integer)
MySeries = 0
For i = 1 To x
MySeries = MySeries + Application.Power(e, i / Application.Fact(i))
Next i
End Function
and use it in cell's formula etc. :-)
0

Author Commented:
Thanks, it works1
0
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