Estimate the value of the function represented by (x,y) data set at an intermediate x-value.

## Syntax

**INTERPOLATE**(**X**, **Y**, **target**, **Method**, **extrapolate**)

- X
- is the x-component of the input data table (a one-dimensional array of cells (e.g., rows or columns)).
- Y
- is the y-component (i.e., function) of the input data table (a one-dimensional array of cells (e.g., rows or columns)).
- target
- is the desired x-value(s) to interpolate for (a single value or a one-dimensional array of cells (e.g., rows or columns)).
- Method
- is the interpolation method (1 = Forward Flat, 2 = Backward Flat, 3 = Linear, 4 = Cubic Spline).
Value Method 1 Forward Flat. 2 Backward Flat. 3 Linear (default). 4 Cubic Spline. - extrapolate
- sets whether or not to allow extrapolation (1 = Yes, 0 = No). If missing, the default is to not allow extrapolation.
Value Extrapolate 0 No (default). 1 Yes.

Warning

INTERPOLATE(.) function is deprecated as of version 1.68.4: use NxINTRPL(.) function instead.

## Remarks

- 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.

## Files Examples

## Related Links

## References

- 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.

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