# RDERIV

## Purpose:

Calculates the derivative of a series using a right-to-left algorithm.

## Syntax:

RDERIV(series, method)

series

-

An interval or XY series, the series to differentiate.

method

-

Optional. An integer, the last point calculation method. Defaults to 0.

 0: last point = s[end]/deltax(s) 1: last point = (s[end]-s[end-1])/deltax(s)

## Returns:

A series or table.

## Example:

W1: 2..5

W2: rderiv(W1)

W3: rderiv(W1, 1)

W2 == {1, 1, 1, 5}

W3 == {1, 1, 1, 1}

W2 and W3 compute the right derivative of the series {2, 3, 4, 5}. The results are identical except for the first point.

## Example:

W1: 2..5;setdeltax(1/10)

W2: rderiv(W1)

W3: rderiv(W1, 1)

W2 == {10, 10, 10, 50}

W3 == {10, 10, 10, 10}

Same as above except the results are multiplied by the inverse of the DELTAX.

## Remarks:

RDERIV computes the 2 point derivative of series s as follows:

For method == 0 (default), the data is assumed to be zero beyond the last sample, thus for a series of N points, the derivative at the last point is computed as:

For method == 1,

The end point treatment of method 1 generally results in a smaller end point discontinuity when the end point of the input data is not near zero.

See LDERIV to compute the 2 point left derivative.

See DERIV to compute the derivative using a quadratic polynomial.

See DIFF to compute the series differences.