Posted by Martin Söderstjerna on March 21, 2001 4:04 AM

Hello!

I´ve got what I think is an easy question about interpolation.

A B

1 0 0,4

2 0,1 0,35

3 0,2 0,31

4 0,3 0,27

5 0,4 0,23

6 0,5 0,20

I wold like Excel to return the value for column B if I now the value for column A. For example A=0,15 gives me B=0,33

Thanks!

Best regards

Martin

Posted by Mark W. on March 21, 2001 5:36 AM

Martin, I have a few questions about your posting.

1. I don't quite understand your data. Are the

comma separated values listed x,y coordinates for

points A and B?

2. If these are coordinates and how are we to

find B given only one point, A? Remember, it

takes 2 points to make a line.

3. Are you confusing interpolation with extrapolation?

Interpolation is an estimate of values between 2

known values which you don't appear to have.

Extrapolation extends a data set beyond known

values.

Posted by Martin Söderstjerna on March 21, 2001 5:57 AM

The values are not coordinates, I'll give you an new example. I've got an table with 40 X-values and the corresponding 40 G(X)-values.

X G(X)

0 40

1 35

2 31

3 28

4 26

I would like to have a function that delivers the G(X) value for all X-values between 0 and 4.

For example

X=0,3 G(X)=...

X=0,53 G(X)=...

X=3,89 G(X)=...

Regards

Martin

Posted by Martin Söderstjerna on March 21, 2001 6:03 AM

Posted by Mark W. on March 21, 2001 6:19 AM

Can you describe function G?

Posted by Mark W. on March 21, 2001 6:27 AM

> I would like to have a function that delivers

> the G(X) value for all X-values between 0 and 4.

...but, isn't there an infinite number of X-values

between 0 and 4?

Posted by Martin Söderstjerna on March 21, 2001 6:35 AM

G(X) is calculated from a normal distribution table, but it's enough if the interpolation is linear. I'll give you a new example:

IF X=10 then G(X)=8

X=12 then G(X)=9

I would like to determine the G(X) value if X=10,5.

Solution:

((10,5-10)/(12-10))*(9-8)+8 makes G(X)=8,25

Posted by Martin Söderstjerna on March 21, 2001 6:40 AM

:There are only 41 X-values (0.1, 0.2, 0.3,..., 3.8, 3.9, 4.0) and of course the corresponding 41 G(X) values.

Posted by Mark W. on March 21, 2001 6:46 AM

Okay, I just woke up! ; )

I just realized that the commas that you're using

are decimal symbols! This array formula should

do the trick:

{=TREND({8;9},{10;12},10.5)}

If you're not familiar with array formulas, they're

entered using the Control+Shift+Enter key

combination. The braces, {}, are not typed by

you -- they're an supplied by Excel as an

indication that you've entered an array formula.

Sorry, it took so long for me to wake up. I

think I'll go re-fill my coffee cup!