abscissae: abscissae of the given data points
ordinates: ordinates of the given data points
targets: abscissae of the interpolated data
interpolation: method of interpolation, defaults to 0 ('linear')
The output consists always of one column of numbers.
Possible interpolation methods are:
1: linear with averaging;
3: staircase with averaging;
4: natural cubic spline;
5: natural cubic spline with averaging.
The abscissae should be given in increasing order. If the abscissae is not in increasing order the INTERPOLATION function is significantly slower. If any two abscissae values are equal an error is returned. If any of interpolation methods 1 ('linear with averaging'), 3 ('staircase with averaging'), and 5 ('natural cubic spline with averaging') is used, the number of returned values is one less than the number of targets and the target values must be given in increasing order. The values returned are the average heights of the interpolation function on the intervals determined by consecutive target values. Strings and empty cells in abscissae and ordinates are ignored. If several target data are provided they must be in the same column in consecutive cells.