Interpolation functions

Analytica User GuideMore Array FunctionsInterpolation functions

These three functions interpolate across arrays. Given arrays y and x with a common index i, these functions interpolate a value for y corresponding to value v along the x axis.

LinearInterp() and CubicInterp() use these variables:

Index_a:

a

b

c

Index_b:

1

2

3

Array_a:

	Index_b ▶
Index_a: ▼	1	2	3
a	7	-3	1
b	-4	-1	6
c	5	0	-2

Stepinterp(x, y, v, i)

Returns the element or slice of array y for which v has the smallest value less than or equal to x. x and y must both be indexed by i, and x must be increasing along index i. If v is greater than all values of x, it returns the element of y for which x has the largest value.

When an optional parameter, LeftLookup, is specified as True, it returns the element or slice of y corresponding to the largest value in x that is less than or equal to v.

If v is an atom (scalar value), the result is an array indexed by all indexes of a except x’s index. If v is an array, the result is also indexed by the indexes of v.

If the first parameter x is an index of y, the fourth parameter is optional. Stepinterp(x, y, v) is similar to y[x = v] except that y[x = v] selects based on v being equal to x, while Stepinterp(x, y, v) selects based on v being greater than or equal to x.

Stepinterp() can be used to perform table lookup.

Library: Array

Examples: To see the values in Car_prices corresponding to Years >= 2007.5:

Stepinterp(Years, Car_prices, 2007.5, Years) →

VW	Honda	BMW
19K	22K	30K

Here v is a list of two values:

Stepinterp(Years, Car_prices, [2007, 2008], Years) →

	VW	Honda	BMW
2007	18K	20K	28K
2008	19K	22K	30K

See Also

Relational tables and multiD arraysInterpolation functionsFourier Transform