nlsr (version 2021.8.19)

dex: Calculate expression for derivative calculations.

Description

Converts input to an expression suitable for use in nlsDeriv and related functions.

Usage

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

Value

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

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.

Author

Duncan Murdoch

Details

If do_substitute is NA, the following rules are used:

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

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

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

4. 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.

Examples

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