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#1
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extrapolate data from series
Hi, Back again! I have a column of data in A running from 1.1 to 16 in 0.1 increments (1.1, 1.2, 1.3, all the way to 16). Next to this column I have a column of data corresponding to each of these points. I am trying to figure out how to extrapolate data from this series in B. For example, I have the value for 1.1, 1.2, 1.3 etc, but I want to work out the value at 1.15, or 1.35. Is it possible to set up a cell where I could put in my point from column A, e.g 1.75 and have it work out what the point would be from the data in column B? Thanks for any help with this, it is basic math, I'm sure, but my values in column B are standard index form to 10 decimal places (e.g 1.2207E-10), so it becomes a bit of head wrecker (for me anyway!) :) -- Micronaut ------------------------------------------------------------------------ Micronaut's Profile: http://www.excelforum.com/member.php...o&userid=15677 View this thread: http://www.excelforum.com/showthread...hreadid=380042 |
#2
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Did you look at the forecats and the trend worksheet functions. =FORECAST(C3,B1:B11,A1:A11) where C3=1.15 Mangesh -- mangesh_yadav ------------------------------------------------------------------------ mangesh_yadav's Profile: http://www.excelforum.com/member.php...o&userid=10470 View this thread: http://www.excelforum.com/showthread...hreadid=380042 |
#3
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Thanks for the reply, much appreciated. My numbers run in rows 2 to 151 (headings in top row). I used =FORECAST(C2,B2:B151,A2:A151) but it isn't the expected value. I filled column C with my mid values (1.15,1.25 etc to 15.5) and used column D for the formula to calculate the values corresponding to the points in column C. I might not be understanding the FORECAST funciton correctly however. I only need to estimate between 1.1 and 1.2, for the 1.15 value, rather than using the entire set of data to estimate. -- Micronaut ------------------------------------------------------------------------ Micronaut's Profile: http://www.excelforum.com/member.php...o&userid=15677 View this thread: http://www.excelforum.com/showthread...hreadid=380042 |
#4
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You are probably looking for this (interpolation) formula: =(C2-LOOKUP(C2,$A$2:$A$12))/(INDEX($A$2:$B$12,MATCH(C2,$A$2:$A$12,1)+1,1)-LOOKUP(C2,$A$2:$A$12))*(INDEX($A$2:$B$12,MATCH(C2, $A$2:$A$12,1)+1,2)-LOOKUP(C2,$A$2:$A$12,$B$2:$B$12))+LOOKUP(C2,$A$2:$ A$12,$B$2:$B$12) Substitute A12 or B12 with your last row 151. Mangesh -- mangesh_yadav ------------------------------------------------------------------------ mangesh_yadav's Profile: http://www.excelforum.com/member.php...o&userid=10470 View this thread: http://www.excelforum.com/showthread...hreadid=380042 |
#5
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Mangesh,
I have come across your response to this thread and you're obviously the person I need to communicate with. I have tried to use your formula but as yet have got nowhere. I have a similar query, I need to interpolate for a value in a table in this case tank volumes and other info. Depth of water is in 20 cm increments in col A with volume and other info in cols B through E I would like to extract info from any given 1 cm increment . Alternatively I can do the maths if someone can tell me how to get the cell above and below my required value in col A for vlookup. Many thanks Ben "mangesh_yadav" wrote: You are probably looking for this (interpolation) formula: =(C2-LOOKUP(C2,$A$2:$A$12))/(INDEX($A$2:$B$12,MATCH(C2,$A$2:$A$12,1)+1,1)-LOOKUP(C2,$A$2:$A$12))*(INDEX($A$2:$B$12,MATCH(C2, $A$2:$A$12,1)+1,2)-LOOKUP(C2,$A$2:$A$12,$B$2:$B$12))+LOOKUP(C2,$A$2:$ A$12,$B$2:$B$12) Substitute A12 or B12 with your last row 151. Mangesh -- mangesh_yadav ------------------------------------------------------------------------ mangesh_yadav's Profile: http://www.excelforum.com/member.php...o&userid=10470 View this thread: http://www.excelforum.com/showthread...hreadid=380042 |
#6
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To get the values above and below I suggest the following:
Below {=3DSUM(--(A1{0,9,19,29})*--(A1<{10,20,30,40})*{0,10,20,30,40})} This will return say 0 if a1 is between 0-9 , 10 if it is between 10- 19 etc etc Above {=3DSUM(--(A1{0,9,19,29})*--(A1<{10,20,30,40})*{10,20,30,40,50})} The result of these formulas would be the lower and upper nodes in your interpolation formula. The linear interp function for the case above would be something like this: interp value =3D X0+ (X0 - X1)/(1.2-1.1) * (1.15-1.1) where X is the data column. They are equivalent to a series of nested IF=B4s with ANDS included, albeit more clean and readble IMHO. Hope this helps |
#7
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Hi Ben,
try something like this: Lets say your table lies in the range A1:B5. And the lookup value lies in A10, then use: =IF(ISNUMBER(MATCH(A10,A1:A5,0)),VLOOKUP(A10,A1:B5 ,2),(A10-OFFSET($A$1,COUNT IF(A1:A5,"<"&A10)-1,0))/(OFFSET($A$1,COUNTIF(A1:A5,"<"&A10),0)-OFFSET($A$1,C OUNTIF(A1:A5,"<"&A10)-1,0))*(OFFSET($A$1,COUNTIF(A1:A5,"<"&A10),1)-OFFSET($A $1,COUNTIF(A1:A5,"<"&A10)-1,1))+OFFSET($A$1,COUNTIF(A1:A5,"<"&A10)-1,1)) Explanation: The above formula consists of the following parts: 1. The first MATCH statement checks if there is a perfect match of the lookup value in the first column, if yes then it uses a VLOOKUP function to get the corresponding value in columns B (note the use of 2 in the vlookup to reference the column B. Since you have upto column E, change this number to 3, 4, or 5 to reference columns C, D, or E) 2. The second part is the interpolation formula which is used incase there is no perfect match. In the offset formula change the last attribute to suit your column. For column B, 1 is used, so for E use 4. The second part works for all values in the column A except for the very first value, for which the vlookup in the first part is used. Mangesh "Ben" wrote in message ... Mangesh, I have come across your response to this thread and you're obviously the person I need to communicate with. I have tried to use your formula but as yet have got nowhere. I have a similar query, I need to interpolate for a value in a table in this case tank volumes and other info. Depth of water is in 20 cm increments in col A with volume and other info in cols B through E I would like to extract info from any given 1 cm increment . Alternatively I can do the maths if someone can tell me how to get the cell above and below my required value in col A for vlookup. Many thanks Ben "mangesh_yadav" wrote: You are probably looking for this (interpolation) formula: =(C2-LOOKUP(C2,$A$2:$A$12))/(INDEX($A$2:$B$12,MATCH(C2,$A$2:$A$12,1)+1,1)-LO OKUP(C2,$A$2:$A$12))*(INDEX($A$2:$B$12,MATCH(C2,$A $2:$A$12,1)+1,2)-LOOKUP(C2 ,$A$2:$A$12,$B$2:$B$12))+LOOKUP(C2,$A$2:$A$12,$B$2 :$B$12) Substitute A12 or B12 with your last row 151. Mangesh -- mangesh_yadav ------------------------------------------------------------------------ mangesh_yadav's Profile: http://www.excelforum.com/member.php...o&userid=10470 View this thread: http://www.excelforum.com/showthread...hreadid=380042 |
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