# Interpolation

• Jul 27th 2009, 10:09 AM
Interpolation
Hi all

I have 4 points with 4 associated values:

2=0.32
5=0.52
10=0.43
30=0.97

What I need to do is expand this list to have a total of 10 points - please could somone point me in the right direction to do this?

Thanks for any information.
• Jul 27th 2009, 10:26 AM
stapel
Are you saying that you have four points, the first being (x, y) = (2, 0.32), and that you are needing to do some sort of regression...?
• Jul 27th 2009, 10:27 AM
Yes thats what I am after

Thanks,
• Jul 27th 2009, 10:35 AM
stapel
What sort of regression are you supposed to find? For instance, an exact cubic polynomial can be put through the four points, but you may have been instructed, or otherwise have knowledge specifying, to use an exponential formula, etc.

Thank you! (Wink)
• Jul 27th 2009, 08:06 PM
Krahl
If i were to use linear interpolation to create a point between 2 and 5, say 3...

3=((5-3)/3)*0.32+((3-2)/3)*0.52=0.3867

and 8 between 5 and 10...

8=((10-8)*0.52)/5+((8-5)*0.43)/5=0.466

this is the linear interpolation used in statistics on the tables.

((upperx-x)*f(lowerx))/(upperx-lowerx)+((x-lowerx)*f(upperx))/(upperx-lowerx)

If thats what is meant by interpolation