dex function

dex

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

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.

Examples

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

Author(s)

Duncan Murdoch