Matching Commands
-----------------

The `a m' (`calc-match') [`match'] function takes a vector of formulas
and a rewrite-rule-style pattern, and produces a vector of all
formulas which match the pattern.  The command prompts you to enter
the pattern; as for `a r', you can enter a single pattern (i.e., a
formula with meta-variables), or a vector of patterns, or a variable
which contains patterns, or you can give a blank response in which
case the patterns are taken from the top of the stack.  The pattern
set will be compiled once and saved if it is stored in a variable.  If
there are several patterns in the set, vector elements are kept if
they match any of the patterns.

For example, `match(a+b, [x, x+y, x-y, 7, x+y+z])' will return `[x+y,
x-y, x+y+z]'.

The `import' mechanism is not available for pattern sets.

The `a m' command can also be used to extract all vector elements
which satisfy any condition: The pattern `x :: x>0' will select all
the positive vector elements.

With the Inverse flag [`matchnot'], this command extracts all vector
elements which do *not* match the given pattern.

There is also a function `matches(X, P)' which evaluates to 1 if
expression X matches pattern P, or to 0 otherwise.  This is sometimes
useful for including into the conditional clauses of other rewrite
rules.

The function `vmatches' is just like `matches', except that if the
match succeeds it returns a vector of assignments to the
meta-variables instead of the number 1.  For example,
`vmatches(f(1,2), f(a,b))' returns `[a := 1, b := 2]'.  If the match
fails, the function returns the number 0.