IDL Reference Guide: Procedures and Functions

DERIV

The DERIV function performs numerical differentiation using 3-point, Lagrangian interpolation.

Syntax

Result = DERIV([X,] Y)

Return Value

Returns the derivative of the numerical differentiation.

Arguments

X

Differentiate with respect to this variable. If omitted, unit spacing for Y (i.e., Xi = i) is assumed.

Y

The variable to be differentiated.

Examples

X = [ 0.1, 0.3, 0.4, 0.7, 0.9]  
Y = [ 1.2, 2.3, 3.2, 4.4, 6.6]  
PRINT, DERIV(Y)  
PRINT, DERIV(X,Y)  

IDL prints:

1.20000   1.00000   1.05000   1.70000   2.70000  
3.16666   7.83333   7.75000   8.20000   13.8000