Question about interpolation

[boxy]

Hi
I have points deffined with x,y and z coordinates.
Now I want to give x, y coordinate of new point and based on othe
points to calculate Z for this new point. How can I do it in Excel
Than

 

[David]

You need to do 2-variable regression. I have used this a lot in the past.
I think it is now an add-in to Excel (I did it in Lotus - excuse me - many
years ago).

This gives you the coefficents of an equation of the type:
z = r1 x + r2 y + r3 (+ possibly r4 x y + r5 x^2 +r6 y^2)

Once you have the coefficeints obviously you can calculate values for any z
of your choice. You probably know that interpolation is more reliable than
extrapolation, so if you need to do the latter be careful!

Regards

David

 

[Tushar Mehta]

As David indicated you can do a surface of best fit analysis. Use XL's
LINEST function.

If you want to do piecewise linear interpolation, you will have to roll
your own function. Alternatively, use LINEST with just the 2 Y values
and the 2 X values that bracket the (x,y) coordinate of interest.

--
Regards,

Tushar Mehta
www.tushar-mehta.com
Microsoft MVP -- Excel