On 2012-07-05, Jorge Calvo <Jorge.Calvo at avemaria.edu> wrote:
> What is the difference between the commands ev, subst, and at?
> If I need to substitute a numerical value for a free variable in a
> simple formula, can they be used interchangeably?
at is like subst, except that at tries to be careful about expressions
which have variables which are conceptually local to the operator, e.g.
the variable i in 'sum(foo(i), i, ...) and the variable x in 'diff(f(x),
x). subst happily replaces such variables, while at creates a noun
expression.
ev subsitutes values (i.e. the thing in a symbol's value slot) for
symbols -- that is, ev evaluates an expression -- however, ev also does
lots of other things, which you might or might not want. I suppose
?meval (internal Lisp function for evaluation) would evaluate without
the multitude of side-effects of ev ....
HTH,
Robert Dodier