Function: vnapply - Make a function from an expression and arguments (replacement for unapply)
expr - any expression
vars - one or more variables (may be any non-constant expressions)
The result of vnapply(expr,x) is a function which, when applied to x , returns the original expression expr .
The "variables" vars may be arbitrary non-constant expressions, but these will only be recognized in expr if they occur there as operands. This is the same behaviour as occurs in subs . Thus vnapply(sin(x+y),x+y) will work, but vnapply(sin(x+y+z),x+y) will not.
This is a replacement for unapply , correcting several problems with that procedure:
- Sometimes unapply returns a result of the form or , vnapply does not. In these cases, the result of unapply will not work under evalhf , while the result of vnapply will.
- vnapply works with expressions that are arrays (including vectors and matrices) or tables, which unapply does not..
- vnapply works with expressions containing derivatives (converting them to D notation), while in many cases unapply does not.
This function is part of the Maple Advisor Database library, and must be loaded before use by the command readlib(vnapply); .
> f1 := unapply(x^2,x); f2 := vnapply(x^2,x);
> f1 := unapply(-cos(x+1),x); f2 := vnapply(-cos(x+1),x);
> f1(3,4); f2(3,4);
Error, (in f1) wrong number (or type) of parameters in function diff
V:= vector([x,x^2]): f1:= unapply(V,x);
Error, (in unapply) variables must be unique and of type name
See also: Problems with unapply , subs , unapply
Maple Advisor Database R. Israel, 1998