SERIESSUM for multivariate polynomial

[belligio]

I developed a polynomial equation with two independent variables... Is it possible to use seriessum with two independent variables? If not, do I have to enter the polynomial equation manually?

FYI, I used this formula to develop the equation: =LINEST($Q$7:$Q$805,$R$7:$R$805^{1,2,3,4,5,6,0,0,0,0,0,0}*$S$7:$S$805^{0,0,0,0,0,0,1,2,3,4,5,6},FALSE,TRUE)

One more thing, if I have to enter the equation manually, is this what that formula looks like?: =x + x^2.... + x^6 + y + y^2... + y^6

Thanks!

[MrShorty]

Since you don't appear to have any cross (xy) terms, it seems like it should be as easy as summing two =SERIESSUM() function: =SERIESSUM(x arguments) + SERIESSUM(y arguments).

[belligio]

Thanks so much for the quick response. A quick follow-up question if that's ok:

How would the SERIESSUM formulas refer to the cells? For example, if I enter the LINEST formula across 13 columns, would the x and y coefficients be separate (i.e., x^6, x^5, ....., x, y^6, y^5, ... y), or would they be together (i.e., x^6, y^6, x^5, y^5, ...., x, y)?

Also, I'm assuming that the SERIESSUM for each variable would only refer to the cells pertaining to that variable?

Thanks again!

[MrShorty]

I'm not sure I understand your question.

The help file for the LINEST() function shows how Excel outputs the data: http://office.microsoft.com/en-us/ex...in=HA010277524 see the table below the description of the arguments and description of statistics. Basically, it is the opposite order of the input. It looks like you are inputting the x's in increasing order (x^1,...,x^6,y^1,...,y^6), so the coefficients should be output in the opposite order (y^6,...,y^1,x^6,...,x^1) [editorial aside: I have always been irritated that Excel inverted the order in this way. I always wished they would have programmed it to output the coefficients in the same order they are input.].

The =SERIESSUM() function ideally will want the coefficients in a contiguous range, so this should work just fine. http://office.microsoft.com/en-us/ex...in=HA010277524

[belligio]

That was my question exactly! I didn't realize it reversed the coefficients, I thought it just ordered them from largest power to smallest power. Now I am getting accurate results.

Thanks again seriously. I couldn't find this answer anywhere on the internet.