CubicInterp

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CubicInterp(d,r,x,I)

Returns the natural cubic spline interpolated values of r along d, interpolating for values of X. The points (r,d) that get interpolated are indexed by I. The values of d must be ascending. The index I is optional when d and r have only one index is common; however, it is recommended that you explicitly specify I, since this will enable your expression to array-abstract if any dimension is ever added to d and r in the future.

Null values are allowed in d and r only in releases later than 4.1.1 (not including 4.1.1). Points having either d or r equal to null are ignored. When x is null, the result is null.

Cubicinterp-graph.png

A cubic interpolation can vary wildly from the actual values of the data points. In the above graph, all the r values are positive, yet the interpolation is as small as -22.5 around x=33. Even if the r values are monotonically increasing, this does not mean that the cubic interpolation will be monotonically increasing. The MonoCubicInterp function is a variation that provides a guarantee of monotonicity.

Library

Array functions

See also

User Guide

Returns the natural cubic spline interpolated values of y along x, interpolating for values of v. x and y must both be indexed by i, and x must be increasing along i.

For each value of v, Cubicinterp() finds the nearest values from x, and using a natural cubic spline between the corresponding values of y, computes the interpolated value. If v is less than the minimum value in x, it returns the first value in y; if v is greater than the maximum value in x, it returns the last value for y.

Library

Array

Example

Cubicinterp(Index_b, Array_a, 1.5, Index_b) →
Index_a >
a b c
0.6875 -2.875 2.219
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