interpolation

[magell]

I have a series of x and corresponding y values and need to find the values in between. An example:

X - values Y-values
1 34
2 31
5 29
9 25
15 18
17 17
18 13
22 8
25 2
26 1

How do I find an interpolated y-value for each x (1, 2, 3, 4, 5, 6, 7, etc)?

 

[Andrew Poulsom]

Look at the Forecast function in help.

 

[Mark W.]

Here are the first 15 rows...

Book1
	A	B	C	D	E	F	G	H	I
1	X-values	Y-values		X-values	Y-values		VLOOKUP	FORECAST
2	1	34		1	34		34	34.27674419
3	2	31		2	31		31	33.00930233
4	5	29		3	31.74186		#N/A	31.74186047
5	9	25		4	30.47442		#N/A	30.4744186
6	15	18		5	29		29	29.20697674
7	17	17		6	27.93953		#N/A	27.93953488
8	18	13		7	26.67209		#N/A	26.67209302
9	22	8		8	25.40465		#N/A	25.40465116
10	25	2		9	25		25	24.1372093
11	26	1		10	22.86977		#N/A	22.86976744
12				11	21.60233		#N/A	21.60232558
13				12	20.33488		#N/A	20.33488372
14				13	19.06744		#N/A	19.06744186
15				14	17.8		#N/A	17.8
16				15	18		18	16.53255814
17				16	15.26512		#N/A	15.26511628
Sheet2

This message was edited by Mark W. on 2002-09-11 07:39

 

[magell]

Thank you! It works except for one thing; my x and y values are not linearly correlated, making the forecasted y-values not following the trend... For each x where I don't have a y-value, I would need to make an interpolation between the closest known y-values... have the feeling it's not such a big problem, but so far I haven't had any success..