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Linear interpolation


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searched and searched and not yet found, and then self-made:

have for creating linear interpolation as a bulk operation in the Excel spreadsheet I made the following function. This can be used freely. I am not liable for any errors, if ye be improved, I would be thrilled commented on the source code and look better.



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• interpolated 'a point from a table of x, y points by the method of linear interpolation
  
• Function Interpol_Lin (Xin As Range, Yin As Range Xtarget As Double)
• Dim n%,% ny 'Xin and Yin Counter
• Dim i%, X_index' loop counter
• 
  
• ny = Yin.Cells.Count
• n = Xin.Cells.Count
• 
  
• 'Check whether the same number x and y points is given
• If n ny <> Then
• Interpol_Lin = CVErr (xlErrRef) 'Uneven counts of Xin and Yin "
• GoTo err_ret
• End If
• 
  
• ReDim x (1 To n) As Double
• ReDim Y (1 To n) As Double
• 
  
• 'abundance x [] and y [] to
• For i = 1 To n
• x (i) = Xin (i)
• Y (i) = yin (i)
• Next i
• i = 1
• 
  
• find 'the correct interval
• Do While (Xtarget> x (i))
• X_index = i
• i = i + 1
• Loop
• 
  
• Interpol_Lin = (Y (X_index + 1) - Y (X_index)) / (x (X_index + 1) - x (X_index)) * (Xtarget - x (X_index)) + Y (X_index)
• 
  
• err_ret:
• 
  
• End Function

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