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34. Rules and Patterns


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34.1 Introduction to Rules and Patterns

This section describes user-defined pattern matching and simplification rules. There are two groups of functions which implement somewhat different pattern matching schemes. In one group are tellsimp, tellsimpafter, defmatch, defrule, apply1, applyb1, and apply2. In the other group are let and letsimp. Both schemes define patterns in terms of pattern variables declared by matchdeclare.

Pattern-matching rules defined by tellsimp and tellsimpafter are applied automatically by the Maxima simplifier. Rules defined by defmatch, defrule, and let are applied by an explicit function call.

There are additional mechanisms for rules applied to polynomials by tellrat, and for commutative and noncommutative algebra in affine package.

Categories:  Simplification · Rules and patterns


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34.2 Functions and Variables for Rules and Patterns

Function: apply1 (expr, rule_1, …, rule_n)

Repeatedly applies rule_1 to expr until it fails, then repeatedly applies the same rule to all subexpressions of expr, left to right, until rule_1 has failed on all subexpressions. Call the result of transforming expr in this manner expr_2. Then rule_2 is applied in the same fashion starting at the top of expr_2. When rule_n fails on the final subexpression, the result is returned.

maxapplydepth is the depth of the deepest subexpressions processed by apply1 and apply2.

See also applyb1, apply2, and let.

Categories:  Rules and patterns

Function: apply2 (expr, rule_1, …, rule_n)

If rule_1 fails on a given subexpression, then rule_2 is repeatedly applied, etc. Only if all rules fail on a given subexpression is the whole set of rules repeatedly applied to the next subexpression. If one of the rules succeeds, then the same subexpression is reprocessed, starting with the first rule.

maxapplydepth is the depth of the deepest subexpressions processed by apply1 and apply2.

See also apply1 and let.

Categories:  Rules and patterns

Function: applyb1 (expr, rule_1, …, rule_n)

Repeatedly applies rule_1 to the deepest subexpression of expr until it fails, then repeatedly applies the same rule one level higher (i.e., larger subexpressions), until rule_1 has failed on the top-level expression. Then rule_2 is applied in the same fashion to the result of rule_1. After rule_n has been applied to the top-level expression, the result is returned.

applyb1 is similar to apply1 but works from the bottom up instead of from the top down.

maxapplyheight is the maximum height which applyb1 reaches before giving up.

See also apply1, apply2, and let.

Categories:  Rules and patterns

Option variable: current_let_rule_package

Default value: default_let_rule_package

current_let_rule_package is the name of the rule package that is used by functions in the let package (letsimp, etc.) if no other rule package is specified. This variable may be assigned the name of any rule package defined via the let command.

If a call such as letsimp (expr, rule_pkg_name) is made, the rule package rule_pkg_name is used for that function call only, and the value of current_let_rule_package is not changed.

Categories:  Rules and patterns

Option variable: default_let_rule_package

Default value: default_let_rule_package

default_let_rule_package is the name of the rule package used when one is not explicitly set by the user with let or by changing the value of current_let_rule_package.

Categories:  Rules and patterns

Function: defmatch  
    defmatch (progname, pattern, x_1, …, x_n)  
    defmatch (progname, pattern)

Defines a function progname(expr, x_1, ..., x_n) which tests expr to see if it matches pattern.

pattern is an expression containing the pattern arguments x_1, …, x_n (if any) and some pattern variables (if any). The pattern arguments are given explicitly as arguments to defmatch while the pattern variables are declared by the matchdeclare function. Any variable not declared as a pattern variable in matchdeclare or as a pattern argument in defmatch matches only itself.

The first argument to the created function progname is an expression to be matched against the pattern and the other arguments are the actual arguments which correspond to the dummy variables x_1, …, x_n in the pattern.

If the match is successful, progname returns a list of equations whose left sides are the pattern arguments and pattern variables, and whose right sides are the subexpressions which the pattern arguments and variables matched. The pattern variables, but not the pattern arguments, are assigned the subexpressions they match. If the match fails, progname returns false.

A literal pattern (that is, a pattern which contains neither pattern arguments nor pattern variables) returns true if the match succeeds.

See also matchdeclare, defrule, tellsimp, and tellsimpafter.

Examples:

Define a function linearp(expr, x) which tests expr to see if it is of the form a*x + b such that a and b do not contain x and a is nonzero. This match function matches expressions which are linear in any variable, because the pattern argument x is given to defmatch.

(%i1) matchdeclare (a, lambda ([e], e#0 and freeof(x, e)), b,
                    freeof(x));
(%o1)                         done
(%i2) defmatch (linearp, a*x + b, x);
(%o2)                        linearp
(%i3) linearp (3*z + (y + 1)*z + y^2, z);
                         2
(%o3)              [b = y , a = y + 4, x = z]
(%i4) a;
(%o4)                         y + 4
(%i5) b;
                                2
(%o5)                          y
(%i6) x;
(%o6)                           x

Define a function linearp(expr) which tests expr to see if it is of the form a*x + b such that a and b do not contain x and a is nonzero. This match function only matches expressions linear in x, not any other variable, because no pattern argument is given to defmatch.

(%i1) matchdeclare (a, lambda ([e], e#0 and freeof(x, e)), b,
                    freeof(x));
(%o1)                         done
(%i2) defmatch (linearp, a*x + b);
(%o2)                        linearp
(%i3) linearp (3*z + (y + 1)*z + y^2);
(%o3)                         false
(%i4) linearp (3*x + (y + 1)*x + y^2);
                             2
(%o4)                  [b = y , a = y + 4]

Define a function checklimits(expr) which tests expr to see if it is a definite integral.

(%i1) matchdeclare ([a, f], true);
(%o1)                         done
(%i2) constinterval (l, h) := constantp (h - l);
(%o2)        constinterval(l, h) := constantp(h - l)
(%i3) matchdeclare (b, constinterval (a));
(%o3)                         done
(%i4) matchdeclare (x, atom);
(%o4)                         done
(%i5) simp : false;
(%o5)                         false
(%i6) defmatch (checklimits, 'integrate (f, x, a, b));
(%o6)                      checklimits
(%i7) simp : true;
(%o7)                         true
(%i8) 'integrate (sin(t), t, %pi + x, 2*%pi + x);
                       x + 2 %pi
                      /
                      [
(%o8)                 I          sin(t) dt
                      ]
                      /
                       x + %pi
(%i9) checklimits (%);
(%o9)    [b = x + 2 %pi, a = x + %pi, x = t, f = sin(t)]

Categories:  Rules and patterns

Function: defrule (rulename, pattern, replacement)

Defines and names a replacement rule for the given pattern. If the rule named rulename is applied to an expression (by apply1, applyb1, or apply2), every subexpression matching the pattern will be replaced by the replacement. All variables in the replacement which have been assigned values by the pattern match are assigned those values in the replacement which is then simplified.

The rules themselves can be treated as functions which transform an expression by one operation of the pattern match and replacement. If the match fails, the rule function returns false.

Categories:  Rules and patterns

Function: disprule  
    disprule (rulename_1, …, rulename_2)  
    disprule (all)

Display rules with the names rulename_1, …, rulename_n, as returned by defrule, tellsimp, or tellsimpafter, or a pattern defined by defmatch. Each rule is displayed with an intermediate expression label (%t).

disprule (all) displays all rules.

disprule quotes its arguments. disprule returns the list of intermediate expression labels corresponding to the displayed rules.

See also letrules, which displays rules defined by let.

Examples:

(%i1) tellsimpafter (foo (x, y), bar (x) + baz (y));
(%o1)                   [foorule1, false]
(%i2) tellsimpafter (x + y, special_add (x, y));
(%o2)                   [+rule1, simplus]
(%i3) defmatch (quux, mumble (x));
(%o3)                         quux
(%i4) disprule (foorule1, "+rule1", quux);
(%t4)        foorule1 : foo(x, y) -> baz(y) + bar(x)

(%t5)          +rule1 : y + x -> special_add(x, y)

(%t6)                quux : mumble(x) -> []

(%o6)                    [%t4, %t5, %t6]
(%i6) ''%;
(%o6) [foorule1 : foo(x, y) -> baz(y) + bar(x), 
     +rule1 : y + x -> special_add(x, y), quux : mumble(x) -> []]

Function: let  
    let (prod, repl, predname, arg_1, …, arg_n)  
    let ([prod, repl, predname, arg_1, …, arg_n], package_name)

Defines a substitution rule for letsimp such that prod is replaced by repl. prod is a product of positive or negative powers of the following terms:

A term to a positive power will only match a term having at least that power. A term to a negative power on the other hand will only match a term with a power at least as negative. In the case of negative powers in prod the switch letrat must be set to true. See also letrat.

If a predicate is included in the let function followed by a list of arguments, a tentative match (i.e. one that would be accepted if the predicate were omitted) is accepted only if predname (arg_1', ..., arg_n') evaluates to true where arg_i' is the value matched to arg_i. The arg_i may be the name of any atom or the argument of any kernel appearing in prod. repl may be any rational expression. If any of the atoms or arguments from prod appear in repl the appropriate substitutions are made.

The global flag letrat controls the simplification of quotients by letsimp. When letrat is false, letsimp simplifies the numerator and denominator of expr separately, and does not simplify the quotient. Substitutions such as n!/n goes to (n-1)! then fail. When letrat is true, then the numerator, denominator, and the quotient are simplified in that order.

These substitution functions allow you to work with several rule packages at once. Each rule package can contain any number of let rules and is referenced by a user-defined name. The command let ([prod, repl, predname, arg_1, ..., arg_n], package_name) adds the rule predname to the rule package package_name. The command letsimp (expr, package_name) applies the rules in package_name. letsimp (expr, package_name1, package_name2, ...) is equivalent to letsimp (expr, package_name1) followed by letsimp (%, package_name2), …

current_let_rule_package is the name of the rule package that is presently being used. This variable may be assigned the name of any rule package defined via the let command. Whenever any of the functions comprising the let package are called with no package name, the package named by current_let_rule_package is used. If a call such as letsimp (expr, rule_pkg_name) is made, the rule package rule_pkg_name is used for that letsimp command only, and current_let_rule_package is not changed. If not otherwise specified, current_let_rule_package defaults to default_let_rule_package.

(%i1) matchdeclare ([a, a1, a2], true)$
(%i2) oneless (x, y) := is (x = y-1)$
(%i3) let (a1*a2!, a1!, oneless, a2, a1);
(%o3)         a1 a2! --> a1! where oneless(a2, a1)
(%i4) letrat: true$
(%i5) let (a1!/a1, (a1-1)!);
                        a1!
(%o5)                   --- --> (a1 - 1)!
                        a1
(%i6) letsimp (n*m!*(n-1)!/m);
(%o6)                      (m - 1)! n!
(%i7) let (sin(a)^2, 1 - cos(a)^2);
                        2               2
(%o7)                sin (a) --> 1 - cos (a)
(%i8) letsimp (sin(x)^4);
                        4           2
(%o8)                cos (x) - 2 cos (x) + 1

Categories:  Rules and patterns

Option variable: letrat

Default value: false

When letrat is false, letsimp simplifies the numerator and denominator of a ratio separately, and does not simplify the quotient.

When letrat is true, the numerator, denominator, and their quotient are simplified in that order.

(%i1) matchdeclare (n, true)$
(%i2) let (n!/n, (n-1)!);
                         n!
(%o2)                    -- --> (n - 1)!
                         n
(%i3) letrat: false$
(%i4) letsimp (a!/a);
                               a!
(%o4)                          --
                               a
(%i5) letrat: true$
(%i6) letsimp (a!/a);
(%o6)                       (a - 1)!

Categories:  Rules and patterns

Function: letrules  
    letrules ()  
    letrules (package_name)

Displays the rules in a rule package. letrules () displays the rules in the current rule package. letrules (package_name) displays the rules in package_name.

The current rule package is named by current_let_rule_package. If not otherwise specified, current_let_rule_package defaults to default_let_rule_package.

See also disprule, which displays rules defined by tellsimp and tellsimpafter.

Categories:  Rules and patterns

Function: letsimp  
    letsimp (expr)  
    letsimp (expr, package_name)  
    letsimp (expr, package_name_1, …, package_name_n)

Repeatedly applies the substitution rules defined by let until no further change is made to expr.

letsimp (expr) uses the rules from current_let_rule_package.

letsimp (expr, package_name) uses the rules from package_name without changing current_let_rule_package.

letsimp (expr, package_name_1, ..., package_name_n) is equivalent to letsimp (expr, package_name_1), followed by letsimp (%, package_name_2), and so on.

Categories:  Rules and patterns

Option variable: let_rule_packages

Default value: [default_let_rule_package]

let_rule_packages is a list of all user-defined let rule packages plus the default package default_let_rule_package.

Categories:  Rules and patterns

Function: matchdeclare (a_1, pred_1, …, a_n, pred_n)

Associates a predicate pred_k with a variable or list of variables a_k so that a_k matches expressions for which the predicate returns anything other than false.

A predicate is the name of a function, or a lambda expression, or a function call or lambda call missing the last argument, or true or all. Any expression matches true or all. If the predicate is specified as a function call or lambda call, the expression to be tested is appended to the list of arguments; the arguments are evaluated at the time the match is evaluated. Otherwise, the predicate is specified as a function name or lambda expression, and the expression to be tested is the sole argument. A predicate function need not be defined when matchdeclare is called; the predicate is not evaluated until a match is attempted.

A predicate may return a Boolean expression as well as true or false. Boolean expressions are evaluated by is within the constructed rule function, so it is not necessary to call is within the predicate.

If an expression satisfies a match predicate, the match variable is assigned the expression, except for match variables which are operands of addition + or multiplication *. Only addition and multiplication are handled specially; other n-ary operators (both built-in and user-defined) are treated like ordinary functions.

In the case of addition and multiplication, the match variable may be assigned a single expression which satisfies the match predicate, or a sum or product (respectively) of such expressions. Such multiple-term matching is greedy: predicates are evaluated in the order in which their associated variables appear in the match pattern, and a term which satisfies more than one predicate is taken by the first predicate which it satisfies. Each predicate is tested against all operands of the sum or product before the next predicate is evaluated. In addition, if 0 or 1 (respectively) satisfies a match predicate, and there are no other terms which satisfy the predicate, 0 or 1 is assigned to the match variable associated with the predicate.

The algorithm for processing addition and multiplication patterns makes some match results (for example, a pattern in which a "match anything" variable appears) dependent on the ordering of terms in the match pattern and in the expression to be matched. However, if all match predicates are mutually exclusive, the match result is insensitive to ordering, as one match predicate cannot accept terms matched by another.

Calling matchdeclare with a variable a as an argument changes the matchdeclare property for a, if one was already declared; only the most recent matchdeclare is in effect when a rule is defined. Later changes to the matchdeclare property (via matchdeclare or remove) do not affect existing rules.

propvars (matchdeclare) returns the list of all variables for which there is a matchdeclare property. printprops (a, matchdeclare) returns the predicate for variable a. printprops (all, matchdeclare) returns the list of predicates for all matchdeclare variables. remove (a, matchdeclare) removes the matchdeclare property from a.

The functions defmatch, defrule, tellsimp, tellsimpafter, and let construct rules which test expressions against patterns.

matchdeclare quotes its arguments. matchdeclare always returns done.

Examples:

A predicate is the name of a function, or a lambda expression, or a function call or lambda call missing the last argument, or true or all.

(%i1) matchdeclare (aa, integerp);
(%o1)                         done
(%i2) matchdeclare (bb, lambda ([x], x > 0));
(%o2)                         done
(%i3) matchdeclare (cc, freeof (%e, %pi, %i));
(%o3)                         done
(%i4) matchdeclare (dd, lambda ([x, y], gcd (x, y) = 1) (1728));
(%o4)                         done
(%i5) matchdeclare (ee, true);
(%o5)                         done
(%i6) matchdeclare (ff, all);
(%o6)                         done

If an expression satisfies a match predicate, the match variable is assigned the expression.

(%i1) matchdeclare (aa, integerp, bb, atom);
(%o1)                         done
(%i2) defrule (r1, bb^aa, ["integer" = aa, "atom" = bb]);
                    aa
(%o2)        r1 : bb   -> [integer = aa, atom = bb]
(%i3) r1 (%pi^8);
(%o3)               [integer = 8, atom = %pi]

In the case of addition and multiplication, the match variable may be assigned a single expression which satisfies the match predicate, or a sum or product (respectively) of such expressions.

(%i1) matchdeclare (aa, atom, bb, lambda ([x], not atom(x)));
(%o1)                         done
(%i2) defrule (r1, aa + bb, ["all atoms" = aa, "all nonatoms" =
               bb]);
bb + aa partitions `sum'
(%o2)  r1 : bb + aa -> [all atoms = aa, all nonatoms = bb]
(%i3) r1 (8 + a*b + sin(x));
(%o3)     [all atoms = 8, all nonatoms = sin(x) + a b]
(%i4) defrule (r2, aa * bb, ["all atoms" = aa, "all nonatoms" =
               bb]);
bb aa partitions `product'
(%o4)   r2 : aa bb -> [all atoms = aa, all nonatoms = bb]
(%i5) r2 (8 * (a + b) * sin(x));
(%o5)    [all atoms = 8, all nonatoms = (b + a) sin(x)]

When matching arguments of + and *, if all match predicates are mutually exclusive, the match result is insensitive to ordering, as one match predicate cannot accept terms matched by another.

(%i1) matchdeclare (aa, atom, bb, lambda ([x], not atom(x)));
(%o1)                         done
(%i2) defrule (r1, aa + bb, ["all atoms" = aa, "all nonatoms" =
               bb]);
bb + aa partitions `sum'
(%o2)  r1 : bb + aa -> [all atoms = aa, all nonatoms = bb]
(%i3) r1 (8 + a*b + %pi + sin(x) - c + 2^n);
                                                     n
(%o3) [all atoms = %pi + 8, all nonatoms = sin(x) + 2  - c + a b]
(%i4) defrule (r2, aa * bb, ["all atoms" = aa, "all nonatoms" =
               bb]);
bb aa partitions `product'
(%o4)   r2 : aa bb -> [all atoms = aa, all nonatoms = bb]
(%i5) r2 (8 * (a + b) * %pi * sin(x) / c * 2^n);
                                                  n
                                         (b + a) 2  sin(x)
(%o5) [all atoms = 8 %pi, all nonatoms = -----------------]
                                                 c

The functions propvars and printprops return information about match variables.

(%i1) matchdeclare ([aa, bb, cc], atom, [dd, ee], integerp);
(%o1)                         done
(%i2) matchdeclare (ff, floatnump, gg, lambda ([x], x > 100));
(%o2)                         done
(%i3) propvars (matchdeclare);
(%o3)             [aa, bb, cc, dd, ee, ff, gg]
(%i4) printprops (ee, matchdeclare);
(%o4)                    [integerp(ee)]
(%i5) printprops (gg, matchdeclare);
(%o5)              [lambda([x], x > 100, gg)]
(%i6) printprops (all, matchdeclare);
(%o6) [lambda([x], x > 100, gg), floatnump(ff), integerp(ee), 
                      integerp(dd), atom(cc), atom(bb), atom(aa)]

Option variable: maxapplydepth

Default value: 10000

maxapplydepth is the maximum depth to which apply1 and apply2 will delve.

Categories:  Function application

Option variable: maxapplyheight

Default value: 10000

maxapplyheight is the maximum height to which applyb1 will reach before giving up.

Categories:  Function application

Function: remlet  
    remlet (prod, name)  
    remlet ()  
    remlet (all)  
    remlet (all, name)

Deletes the substitution rule, prod -> repl, most recently defined by the let function. If name is supplied the rule is deleted from the rule package name.

remlet() and remlet(all) delete all substitution rules from the current rule package. If the name of a rule package is supplied, e.g. remlet (all, name), the rule package name is also deleted.

If a substitution is to be changed using the same product, remlet need not be called, just redefine the substitution using the same product (literally) with the let function and the new replacement and/or predicate name. Should remlet (prod) now be called the original substitution rule is revived.

See also remrule, which removes a rule defined by tellsimp or tellsimpafter.

Categories:  Rules and patterns

Function: remrule  
    remrule (op, rulename)  
    remrule (op, all)

Removes rules defined by tellsimp or tellsimpafter.

remrule (op, rulename) removes the rule with the name rulename from the operator op. When op is a built-in or user-defined operator (as defined by infix, prefix, etc.), op and rulename must be enclosed in double quote marks.

remrule (op, all) removes all rules for the operator op.

See also remlet, which removes a rule defined by let.

Examples:

(%i1) tellsimp (foo (aa, bb), bb - aa);
(%o1)                   [foorule1, false]
(%i2) tellsimpafter (aa + bb, special_add (aa, bb));
(%o2)                   [+rule1, simplus]
(%i3) infix ("@@");
(%o3)                          @@
(%i4) tellsimp (aa @@ bb, bb/aa);
(%o4)                   [@@rule1, false]
(%i5) tellsimpafter (quux (%pi, %e), %pi - %e);
(%o5)                  [quuxrule1, false]
(%i6) tellsimpafter (quux (%e, %pi), %pi + %e);
(%o6)             [quuxrule2, quuxrule1, false]
(%i7) [foo (aa, bb), aa + bb, aa @@ bb, quux (%pi, %e),
       quux (%e, %pi)];
                                     bb
(%o7) [bb - aa, special_add(aa, bb), --, %pi - %e, %pi + %e]
                                     aa
(%i8) remrule (foo, foorule1);
(%o8)                          foo
(%i9) remrule ("+", ?\+rule1);
(%o9)                           +
(%i10) remrule ("@@", ?\@\@rule1);
(%o10)                         @@
(%i11) remrule (quux, all);
(%o11)                        quux
(%i12) [foo (aa, bb), aa + bb, aa @@ bb, quux (%pi, %e),
        quux (%e, %pi)];
(%o12) [foo(aa, bb), bb + aa, aa @@ bb, quux(%pi, %e), 
                                         quux(%e, %pi)]

Categories:  Rules and patterns

Function: tellsimp (pattern, replacement)

is similar to tellsimpafter but places new information before old so that it is applied before the built-in simplification rules.

tellsimp is used when it is important to modify the expression before the simplifier works on it, for instance if the simplifier "knows" something about the expression, but what it returns is not to your liking. If the simplifier "knows" something about the main operator of the expression, but is simply not doing enough for you, you probably want to use tellsimpafter.

The pattern may not be a sum, product, single variable, or number.

The system variable rules is the list of rules defined by defrule, defmatch, tellsimp, and tellsimpafter.

Examples:

(%i1) matchdeclare (x, freeof (%i));
(%o1)                         done
(%i2) %iargs: false$
(%i3) tellsimp (sin(%i*x), %i*sinh(x));
(%o3)                 [sinrule1, simp-%sin]
(%i4) trigexpand (sin (%i*y + x));
(%o4)         sin(x) cos(%i y) + %i cos(x) sinh(y)
(%i5) %iargs:true$
(%i6) errcatch(0^0);
 0
0  has been generated
(%o6)                          []
(%i7) ev (tellsimp (0^0, 1), simp: false);
(%o7)                  [^rule1, simpexpt]
(%i8) 0^0;
(%o8)                           1
(%i9) remrule ("^", %th(2)[1]);
(%o9)                           ^
(%i10) tellsimp (sin(x)^2, 1 - cos(x)^2);
(%o10)                 [^rule2, simpexpt]
(%i11) (1 + sin(x))^2;
                                      2
(%o11)                    (sin(x) + 1)
(%i12) expand (%);
                                   2
(%o12)               2 sin(x) - cos (x) + 2
(%i13) sin(x)^2;
                                  2
(%o13)                     1 - cos (x)
(%i14) kill (rules);
(%o14)                        done
(%i15) matchdeclare (a, true);
(%o15)                        done
(%i16) tellsimp (sin(a)^2, 1 - cos(a)^2);
(%o16)                 [^rule3, simpexpt]
(%i17) sin(y)^2;
                                  2
(%o17)                     1 - cos (y)

Categories:  Rules and patterns

Function: tellsimpafter (pattern, replacement)

Defines a simplification rule which the Maxima simplifier applies after built-in simplification rules. pattern is an expression, comprising pattern variables (declared by matchdeclare) and other atoms and operators, considered literals for the purpose of pattern matching. replacement is substituted for an actual expression which matches pattern; pattern variables in replacement are assigned the values matched in the actual expression.

pattern may be any nonatomic expression in which the main operator is not a pattern variable; the simplification rule is associated with the main operator. The names of functions (with one exception, described below), lists, and arrays may appear in pattern as the main operator only as literals (not pattern variables); this rules out expressions such as aa(x) and bb[y] as patterns, if aa and bb are pattern variables. Names of functions, lists, and arrays which are pattern variables may appear as operators other than the main operator in pattern.

There is one exception to the above rule concerning names of functions. The name of a subscripted function in an expression such as aa[x](y) may be a pattern variable, because the main operator is not aa but rather the Lisp atom mqapply. This is a consequence of the representation of expressions involving subscripted functions.

Simplification rules are applied after evaluation (if not suppressed through quotation or the flag noeval). Rules established by tellsimpafter are applied in the order they were defined, and after any built-in rules. Rules are applied bottom-up, that is, applied first to subexpressions before application to the whole expression. It may be necessary to repeatedly simplify a result (for example, via the quote-quote operator '' or the flag infeval) to ensure that all rules are applied.

Pattern variables are treated as local variables in simplification rules. Once a rule is defined, the value of a pattern variable does not affect the rule, and is not affected by the rule. An assignment to a pattern variable which results from a successful rule match does not affect the current assignment (or lack of it) of the pattern variable. However, as with all atoms in Maxima, the properties of pattern variables (as declared by put and related functions) are global.

The rule constructed by tellsimpafter is named after the main operator of pattern. Rules for built-in operators, and user-defined operators defined by infix, prefix, postfix, matchfix, and nofix, have names which are Lisp identifiers. Rules for other functions have names which are Maxima identifiers.

The treatment of noun and verb forms is slightly confused. If a rule is defined for a noun (or verb) form and a rule for the corresponding verb (or noun) form already exists, the newly-defined rule applies to both forms (noun and verb). If a rule for the corresponding verb (or noun) form does not exist, the newly-defined rule applies only to the noun (or verb) form.

The rule constructed by tellsimpafter is an ordinary Lisp function. If the name of the rule is $foorule1, the construct :lisp (trace $foorule1) traces the function, and :lisp (symbol-function '$foorule1) displays its definition.

tellsimpafter quotes its arguments. tellsimpafter returns the list of rules for the main operator of pattern, including the newly established rule.

See also matchdeclare, defmatch, defrule, tellsimp, let, kill, remrule, and clear_rules.

Examples:

pattern may be any nonatomic expression in which the main operator is not a pattern variable.

(%i1) matchdeclare (aa, atom, [ll, mm], listp, xx, true)$
(%i2) tellsimpafter (sin (ll), map (sin, ll));
(%o2)                 [sinrule1, simp-%sin]
(%i3) sin ([1/6, 1/4, 1/3, 1/2, 1]*%pi);
                    1  sqrt(2)  sqrt(3)
(%o3)              [-, -------, -------, 1, 0]
                    2     2        2
(%i4) tellsimpafter (ll^mm, map ("^", ll, mm));
(%o4)                  [^rule1, simpexpt]
(%i5) [a, b, c]^[1, 2, 3];
                                2   3
(%o5)                      [a, b , c ]
(%i6) tellsimpafter (foo (aa (xx)), aa (foo (xx)));
(%o6)                   [foorule1, false]
(%i7) foo (bar (u - v));
(%o7)                    bar(foo(u - v))

Rules are applied in the order they were defined. If two rules can match an expression, the rule which was defined first is applied.

(%i1) matchdeclare (aa, integerp);
(%o1)                         done
(%i2) tellsimpafter (foo (aa), bar_1 (aa));
(%o2)                   [foorule1, false]
(%i3) tellsimpafter (foo (aa), bar_2 (aa));
(%o3)              [foorule2, foorule1, false]
(%i4) foo (42);
(%o4)                       bar_1(42)

Pattern variables are treated as local variables in simplification rules. (Compare to defmatch, which treats pattern variables as global variables.)

(%i1) matchdeclare (aa, integerp, bb, atom);
(%o1)                         done
(%i2) tellsimpafter (foo(aa, bb), bar('aa=aa, 'bb=bb));
(%o2)                   [foorule1, false]
(%i3) bb: 12345;
(%o3)                         12345
(%i4) foo (42, %e);
(%o4)                 bar(aa = 42, bb = %e)
(%i5) bb;
(%o5)                         12345

As with all atoms, properties of pattern variables are global even though values are local. In this example, an assignment property is declared via define_variable. This is a property of the atom bb throughout Maxima.

(%i1) matchdeclare (aa, integerp, bb, atom);
(%o1)                         done
(%i2) tellsimpafter (foo(aa, bb), bar('aa=aa, 'bb=bb));
(%o2)                   [foorule1, false]
(%i3) foo (42, %e);
(%o3)                 bar(aa = 42, bb = %e)
(%i4) define_variable (bb, true, boolean);
(%o4)                         true
(%i5) foo (42, %e);
Error: bb was declared mode boolean, has value: %e
 -- an error.  Quitting.  To debug this try debugmode(true);

Rules are named after main operators. Names of rules for built-in and user-defined operators are Lisp identifiers, while names for other functions are Maxima identifiers.

(%i1) tellsimpafter (foo (%pi + %e), 3*%pi);
(%o1)                   [foorule1, false]
(%i2) tellsimpafter (foo (%pi * %e), 17*%e);
(%o2)              [foorule2, foorule1, false]
(%i3) tellsimpafter (foo (%i ^ %e), -42*%i);
(%o3)         [foorule3, foorule2, foorule1, false]
(%i4) tellsimpafter (foo (9) + foo (13), quux (22));
(%o4)                   [+rule1, simplus]
(%i5) tellsimpafter (foo (9) * foo (13), blurf (22));
(%o5)                  [*rule1, simptimes]
(%i6) tellsimpafter (foo (9) ^ foo (13), mumble (22));
(%o6)                  [^rule1, simpexpt]
(%i7) rules;
(%o7) [foorule1, foorule2, foorule3, +rule1, *rule1, ^rule1]
(%i8) foorule_name: first (%o1);
(%o8)                       foorule1
(%i9) plusrule_name: first (%o4);
(%o9)                        +rule1
(%i10) remrule (foo, foorule1);
(%o10)                         foo
(%i11) remrule ("^", ?\^rule1);
(%o11)                          ^
(%i12) rules;
(%o12)        [foorule2, foorule3, +rule1, *rule1]

A worked example: anticommutative multiplication.

(%i1) gt (i, j) := integerp(j) and i < j;
(%o1)           gt(i, j) := integerp(j) and i < j
(%i2) matchdeclare (i, integerp, j, gt(i));
(%o2)                         done
(%i3) tellsimpafter (s[i]^^2, 1);
(%o3)                 [^^rule1, simpncexpt]
(%i4) tellsimpafter (s[i] . s[j], -s[j] . s[i]);
(%o4)                   [.rule1, simpnct]
(%i5) s[1] . (s[1] + s[2]);
(%o5)                    s  . (s  + s )
                          1     2    1
(%i6) expand (%);
(%o6)                      1 - s  . s
                                2    1
(%i7) factor (expand (sum (s[i], i, 0, 9)^^5));
(%o7) 100 (s  + s  + s  + s  + s  + s  + s  + s  + s  + s )
            9    8    7    6    5    4    3    2    1    0

Categories:  Rules and patterns

Function: clear_rules ()

Executes kill (rules) and then resets the next rule number to 1 for addition +, multiplication *, and exponentiation ^.

Categories:  Rules and patterns


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This document was generated by Jaime Villate on November, 25 2014 using texi2html 1.76.