IRIS Toolbox Reference Manual

## difflog

First log-difference pseudofunction

#### Syntax

    difflog(EXPR)
    difflog(EXPR,K)

#### Description

If the input argument `K` is not specified, this pseudofunction expands to

    (log(EXPR)-log(EXPR{-1}))

If the input argument `K` is specified, it expands to

    (log(EXPR)-log(EXPR{K}))

The two derived expressions, `EXPR{-1}` and `EXPR{K}`, are based on `EXPR`, and have all its time subscripts shifted by --1 or by `K` periods, respectively.

#### Example

The following two lines of code

    difflog(Z)
    difflog(X{1}/Y{-1},-2)

will expand to

    (log(Z)-log(Z{-1}))
    (log(X{1}/Y{-1})-log(X{-1}/Y{-3}))

IRIS Toolbox. Copyright © 2007—2013 Jaromir Benes.