Why are you reinventing the wheel? LINEST does this.
http://www.stfx.ca/people/bliengme/E...Polynomial.htm

Depending on where your data lives, you can use one of the following
approaches from VBA
http://www.google.com/groups?selm=VA...37cab0%40t8000
http://www.google.com/groups?selm=ue...GP10.phx.gb l

These approaches can be adapted to MMULT and MMINVERSE if you really
want to do it manually.

Jerry

Mark Schreiber wrote:

I am trying to write a VBA User-defined function to develop a

quadratic curve-fit formula. It can be done on the spreadsheet

itself by creating a 3x3 square array of {X, X^2, X^3 ...} terms, and

a 3x1 vector array of {Y, XY, X^2Y} terms, then using the spreadsheet

function {=MMULT(MINVERSE(X_SquareArray),XY_VectorArray)}. This will

yield the coefficients for a quadratic polynomial y=b0 + b1*x +

b2*x^2. However, I have a number of datasets containing (X,Y)

ordered pairs, and don't want to devote a lot of spreadsheet space to

creating these arrays. Instead, I want to do all the matrix

multiplication down to obtaining the coefficients within the

user-defined function. Then the final step will be to set the

function value equal to the polynomial equation, using an input value

for x. Does anyone know how to do this trick?