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INTERP

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Purpose

General-purpose interpolation

Synopsis

INTERP(X, X1, Y1, X2, Y2, ..., Xn, Yn)

Arguments

X	X-value to be interpolated.
Xi, Yi	Pairs of values for the interpolation. The Xi must be in increasing order.

Example

Typically X will be a variable and the interpolation pairs (X_i,Y_i) are given in an XV. Given the following matrix items:

Column: Total
XV    : XVI: = = 0
             = = 0
             = = 1
             = = 1
             = = 2
             = = 4
             = = 3
             = = 9

then the following formula interpolates X:

= INTERP ( X, XVI )

Further information

In the above example, if X has a current value of 1.5, then the function will be evaluated as 2.5 (X is halfway between X=1 and X=2, so the result is halfway between Y=1 and Y=4). As can be seen, the points in this case are the squares of the integers, so the function is approximating the square of X by interpolation.

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