Estimate the value of the function represented by (x,y) data set at an intermediate x-value.
INTERPOLATE(X, Y, target, Method, extrapolate)
- is the x-component of the input data table (a one dimensional array of cells (e.g. rows or columns)).
- is the y-component (i.e. function) of the input data table (a one dimensional array of cells (e.g. rows or columns)).
- is the desired x-value(s) to interpolate for (a single value or a one dimensional array of cells (e.g. rows or columns)).
- is the interpolation method (1=Forward Flat, 2=Backward Flat, 3=Linear, 4=Cubic Spline).
- sets whether or not to allow extrapolation (1=Yes, 0=No). If missing, the default is to not allow extrapolation.
- The X and Y array sizes must be identical.
- The X-array and Y-array both consist of numerical values. Dates in Excel are internally represented by numbers.
- The values in the X-array can be unsorted and may have duplicate values.
- In the case where X has duplicate values, INTERPOLATE will replace those duplicate values with a single entry, setting the corresponding y-value equal to the average.
- The X and/or Y arrays may have missing values (#N/A). In this case, INTERPOLATE will remove those entries.
- For cubic spline interpolation, we construct a set of natural cubic splines that are twice continuously differentiable functions to yield the least oscillation about the function f which is interpolated.
Example 1: *Interpolation (ordered X and no missing values)
Example 2: *Extrapolation (ordered X and no missing values)
Example 3: *Interpolation (un-ordered X and no missing values)
Example 4: *Interpolation (un-ordered X, no duplicates, and with missing values)
Example 5: *Interpolation (un-ordered X, with duplicates, and no missing values)
- Kincaid, David; Ward Cheney (2002). Numerical Analysis (3rd edition). Brooks/Cole. ISBN 0-534-38905-8. Chapter 6.
- Ahlberg, Nielson, and Walsh, The Theory of Splines and Their Applications, 1967.