## INTERPOL

The INTERPOL function performs linear interpolation on vectors with a regular or irregular grid. The result is a single- or double-precision floating-point vector, or a complex vector if the input vector is complex.

This routine is written in the IDL language. Its source code can be found in the file ``` interpol.pro``` in the ``` lib``` subdirectory of the IDL distribution.

### Calling Sequence

; For regular grids: Result = INTERPOL( V, N );

; For irregular grids: Result = INTERPOL( V, X, U );

### Arguments

#### V

An input vector of any type except string.

#### N

The number of points in the result when both input and output grids are regular. The abscissa values for the output grid will contain the same endpoints as the input.

#### X

The abscissa values for V , in the irregularly-gridded case. X must have the same number of elements as V , and the values must be monotonically ascending or descending.

#### U

The abscissa values for the result. The result will have the same number of elements as U . U does not need to be monotonic.

### Example

Create a floating-point vector of 61 elements in the range [-3, 3].

X = FINDGEN(61)/10 - 3

V = SIN(X) ; Evaluate V[x] at each point .

U = [-2.50, -2.25, -1.85, -1.55, -1.20, -0.85, -0.50, -0.10, \$

0.30, 0.40, 0.75, 0.85, 1.05, 1.45, 1.85, 2.00, 2.25, 2.75 ]
; Define X-values where interpolates are desired.

result = INTERPOL(V, X, U) ; Interpolate.

PLOT, X, V ; Plot the function.

OPLOT, U, result ; Plot the interpolated values.