# 16.1 Interpolate/Extrapolate

## Overview Interpolation/extrapolation is a method of estimating and constructing new data points from a discrete set of known data points. This function generates a uniform linearly spaced interpolated curve by one of four methods: Linear, Cubic Spline, Cubic B-Spline, and Akima Spline.

In Origin, the interpolation tool also supports Apparent Interpolation so it can interpolate data according to current axis settings. 1. Create a new worksheet with input data.
2. Select Analysis: Mathematics: Interpolate/Extrapolate.... This opens interp1XY dialog box.

The dialog box calls the interp1xy X-Function to perform the interpolate/extrapolate calculation.

## Dialog Options

Recalculate Controls recalculation of analysis results: None Auto Manual For more information, see: Recalculating Analysis Results Specifies the XY range to be interpolated. For help with range controls, see: Specifying Your Input Data Specify the interpolation/extrapolation method. Linear Linear interpolation is a fast method of estimating a data point by constructing a line between two neighboring data points. This method is generally less accurate than more computationally-intensive methods. Cubic Spline This method splits the input data into a given number of pieces, and fits each segment with a cubic polynomial. The second derivative of each cubic function is set equal to zero. With these boundary conditions met, an entire function can be constructed in a piece-wise manner. Cubic B-Spline This method also splits the input data into pieces, each segment is fitted with discrete Bezier splines. Akima Spline This method is based on a piecewise function composed of a set of polynomials. The Akima interpolation is stable to outliers. Specifies the number of interpolated points. The minimum X value of interpolated curve. The maximum X value of interpolated curve. Boundary condition is only available in Cubic Spline method. Natural 2nd derivatives are 0 on both ends. Not-A-Knot 3rd derivatives are continuous on the second and last-second point. A non-negative parameter that specifies the smoothness of the interpolated curve in Cubic B-Spline interpolation. The factor helps user control the balance between the smoothing and closeness. Larger values will result in smoother curves. Smoothing is only available in Cubic B-Spline method. Spline coefficients when using spline or B-spline method. Available only when the interpolation is performed on a graph. If selected, interpolation is performed using apparent values when the axes scale type has been changed (from linear to log10, for instance). Specifies the output XY data range.

## Algorithm

For algorithm details, please refer to Interpolate Extrapolate Y from X.

## References

For reference details, please refer to Interpolate/Extrapolate Y from X.