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Interpolate ( x1 ; y1 ; x2 ; y2 ; x )

Linear interpolation or extrapolation from two coordinate points

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Bill Holt Notesoft http://www.notesoft.com

  Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

// Interpolation ( x1 ; y1 ; x2 ; y2 ; x ) // Given two coordinate pairs, this function does a linear interpolation, or extrapolation, // depending on whether the unknown x is between or outside of the pair of coordinates. // If the coordinates define a vertical line, an error message is returned. // If any of the required coordinate data is missing, an error message is returned. // Prerequisites: none Case( not IsEmpty ( x1 ) and not IsEmpty ( y1 ) and (x1 = x2) and (y1 = y2) and (x1 = x) ; y1 ; (x1 = x2) ; "error" ; IsEmpty ( x1 ) or IsEmpty ( x2 ) or IsEmpty ( y1 ) or IsEmpty ( y2 ) ; "error" ; (y1 = y2) ; y1 ; (y2-y1)*(x-x1)/(x2-x1) + y1) Click to copy

Given any two xy coordinates, this function will interpolate or extrapolate, linearly, to return the value of y for any known value of x. If the pair of points define a vertical line, or the first point is duplicated, or if one or more of the required entries are missing, the function returns the word "error".

rev: description and notation clarifications

 

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