# dex: dex In nlsr: Functions for Nonlinear Least Squares Solutions - Updated 2022

 dex R Documentation

## dex

### Description

Calculate expression for derivative calculations. Mainly for internal use, `dex()` converts its input to an expression suitable for use in `nlsDeriv` and related functions.

### Usage

``````dex(x, do_substitute = NA, verbose = FALSE)
``````

### Arguments

 `x` An expression represented in a variety of ways. See Details. `do_substitute` Whether to use the expression passed as `x`, or to evaluate it and use its value. `verbose` Print messages describing the process.

### Details

If `do_substitute` is `NA`, the following rules are used:

• An attempt is made to evaluate `x`. If that fails, the expression is used.

• If the evaluation succeeds and the value is a character vector, it is parsed.

• If the value is not a character vector and the expression is a single name, the value is used.

Otherwise, the expression is used.

Once the expression is determined it may be simplified, by extracting the language object from a length-one expression vector, or the right-hand-side from a formula.

Normally a warning will be issued if `x` is a formula containing a left-hand side. To suppress this, wrap the formula in `expression()`, or pass it as a character string to be parsed.

### value

An expression or language object suitable as input to `nlsDeriv` and related functions.

Duncan Murdoch

### Examples

``````   aa <- dex(~ x^2)
aa
str(aa)
bb <- dex(expression(x^2))
bb
str(bb)
cc <- dex("x^2")
cc
str(cc)

``````

nlsr documentation built on Sept. 8, 2023, 5:48 p.m.