Apache OpenOffice (AOO) Bugzilla – Issue 95135

Add function for computing linear interpolation of values

Last modified: 2017-05-20 09:56:13 UTC

Given a range of x-values and a range of y-values, a function would be useful that uses these ranges to compute a y-value for a given x-value using linear interpolation. Example: Row/Column A B 1 3 1 2 5 3 3 6 8 4 10 4 5 12 6 In another cell I would then like to use the function LINEARINTERPOLATION: =LINEARINTERPOLATION(A1:A5; B1:B5; 4) which would evaluate to 2 because the linear interpolation from point (3,1) to (5,3) is (4,2). 3 and 5 are the closest neighbors to 4. =LINEARINTERPOLATION(A1:A5; B1:B5; 8) would evaluate to 6. This is a feature that can be created with the current functions of OpenOffice.org, but it's too complicated. Also it's a feature that Excel doesn't have, but is commonly requested (http://www.google.com/search?q=excel+linear+interpolation).

I confirm it's very hard to design a formula to do linear interpolation. The best way is to use a function. Some time ago (OOo 2.x) I wrote such kind of function. Here is my code, you can use and adapt it (sorry comments are in French) : function interpoler (X as variant, Y as variant, T as double) ' on verifie si on a bien des ARRAY if NOT (IsArray( X ) AND IsArray( Y )) then Err = 519 interpoler = "#VALUE" else Dim debut as integer, fin as integer, length as Integer Dim result As Double debut = LBound(X) fin = UBound(X) length = fin-debut Dim X1 as double, X2 as double, Y1 as double, Y2 as double 'on suppose que X est triÃ© par ordre croissant If (t < X(debut,1)) then 'avant on prend la premiÃ¨re valeur interpoler = Y(debut,1) 'interpoler = "#VALEUR !" Exit function End if If (t >= X(fin,1)) then 'aprÃ¨s on garde la derniÃ¨re valeur interpoler = Y(fin,1) 'interpoler = "#VALEUR !" Exit function End if 'X1 = X(debut,1) For i = 0 to length-1 If (X(debut+i,1) <= t AND X(debut+i+1,1) > t) then X1 = X(debut+i,1) X2 = X(debut+i+1,1) Y1 = Y(debut+i,1) Y2 = Y(debut+i+1,1) Exit For End if Next 'interpolation linÃ©aire interpoler = y1 + (y2-y1)/(x2-x1)*(t-x1) end if End Function

I would also like to see this funcitonality in OOo, I give it 2 votes. Further, it would be nice to see OOo one step ahead of excel when it comes to common requested features. Meanwhile I found another site describing how to build this piecewise linear function, take a look at the bottom of http://www.tutorialsforopenoffice.org/tutorial/LookUp_Functions_In_Calc.html#8.What's In The Middle_|outline Has anyone seen an extension providing this functionality? Jarl

Created attachment 76177 [details] Linear interpolation example This file shows how to implement linear interpolation without doing any complex function or complex formulas. Uses LOOKUP and basic math.

Moved to https://wiki.openoffice.org/wiki/Extensions/Ideas/Calc