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...

******** ******************** ************************************************************************>

Microsoft Excel - Book1 ___Running: xl2000 : OS = Windows NT 4
(F)ile (E)dit (V)iew (I)nsert (O)ptions (T)ools (D)ata (W)indow (H)elp (A)bout
E2G2H2E3G3H3E4G4H4E5G5H5E6G6H6E7G7H7E8G8H8E9G9H9E10G10H10E11G11H11E12G12H12E13G13H13E14G14H14E15G15H15E16G16H16E17G17H17 =
	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 *

[HtmlMaker 2.20] To see the formula in the cells just click on the cells hyperlink or click the Name box
PLEASE DO NOT QUOTE THIS TABLE IMAGE ON SAME PAGE! OTHEWISE, ERROR OF JavaScript OCCUR.

[ 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..