Default

Default[f], if defined, gives the default value for arguments of the function f obtained with a _. pattern object.

Default[f, i] gives the default value to use when _. appears as the i argument of f.

Default[f, i, n] gives the default value for the i argument out of a total of n arguments.

_. represents an optional argument to a function, with a default value specified by Default.

The necessary values for Default[f] must always be defined before _. is used as an argument of f.

Values defined for Default[f] are stored with the Options values of f.

See The Mathematica Book: Section A.5.1.

See also: Options.

Related package: Utilities`FilterOptions`.