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6. Expressions


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6.1 Introduction to Expressions

There are a number of reserved words which should not be used as variable names. Their use would cause a possibly cryptic syntax error.

integrate            next           from                 diff            
in                   at             limit                sum             
for                  and            elseif               then            
else                 do             or                   if              
unless               product        while                thru            
step                                                                     

Most things in Maxima are expressions. A sequence of expressions can be made into an expression by separating them by commas and putting parentheses around them. This is similar to the C comma expression.

(%i1) x: 3$
(%i2) (x: x+1, x: x^2);
(%o2)                          16
(%i3) (if (x > 17) then 2 else 4);
(%o3)                           4
(%i4) (if (x > 17) then x: 2 else y: 4, y+x);
(%o4)                          20

Even loops in Maxima are expressions, although the value they return is the not too useful done.

(%i1) y: (x: 1, for i from 1 thru 10 do (x: x*i))$
(%i2) y;
(%o2)                         done

Whereas what you really want is probably to include a third term in the comma expression which actually gives back the value.

(%i3) y: (x: 1, for i from 1 thru 10 do (x: x*i), x)$
(%i4) y;
(%o4)                        3628800


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6.2 Nouns and Verbs

Maxima distinguishes between operators which are "nouns" and operators which are "verbs". A verb is an operator which can be executed. A noun is an operator which appears as a symbol in an expression, without being executed. By default, function names are verbs. A verb can be changed into a noun by quoting the function name or applying the nounify function. A noun can be changed into a verb by applying the verbify function. The evaluation flag nouns causes ev to evaluate nouns in an expression.

The verb form is distinguished by a leading dollar sign $ on the corresponding Lisp symbol. In contrast, the noun form is distinguished by a leading percent sign % on the corresponding Lisp symbol. Some nouns have special display properties, such as 'integrate and 'derivative (returned by diff ), but most do not. By default, the noun and verb forms of a function are identical when displayed. The global flag noundisp causes Maxima to display nouns with a leading quote mark '.

See also noun, nouns, nounify, and verbify.

Examples:

(%i1) foo (x) := x^2;
                                     2
(%o1)                     foo(x) := x
(%i2) foo (42);
(%o2)                         1764
(%i3) 'foo (42);
(%o3)                        foo(42)
(%i4) 'foo (42), nouns;
(%o4)                         1764
(%i5) declare (bar, noun);
(%o5)                         done
(%i6) bar (x) := x/17;
                                     x
(%o6)                    ''bar(x) := --
                                     17
(%i7) bar (52);
(%o7)                        bar(52)
(%i8) bar (52), nouns;
                               52
(%o8)                          --
                               17
(%i9) integrate (1/x, x, 1, 42);
(%o9)                        log(42)
(%i10) 'integrate (1/x, x, 1, 42);
                             42
                            /
                            [   1
(%o10)                      I   - dx
                            ]   x
                            /
                             1
(%i11) ev (%, nouns);
(%o11)                       log(42)

Categories:  Evaluation · Nouns and verbs


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6.3 Identifiers

Maxima identifiers may comprise alphabetic characters, plus the numerals 0 through 9, plus any special character preceded by the backslash \ character.

A numeral may be the first character of an identifier if it is preceded by a backslash. Numerals which are the second or later characters need not be preceded by a backslash.

Characters may be declared alphabetic by the declare function. If so declared, they need not be preceded by a backslash in an identifier. The alphabetic characters are initially A through Z, a through z, %, and _.

Maxima is case-sensitive. The identifiers foo, FOO, and Foo are distinct. See Lisp and Maxima for more on this point.

A Maxima identifier is a Lisp symbol which begins with a dollar sign $. Any other Lisp symbol is preceded by a question mark ? when it appears in Maxima. See Lisp and Maxima for more on this point.

Examples:

(%i1) %an_ordinary_identifier42;
(%o1)               %an_ordinary_identifier42
(%i2) embedded\ spaces\ in\ an\ identifier;
(%o2)           embedded spaces in an identifier
(%i3) symbolp (%);
(%o3)                         true
(%i4) [foo+bar, foo\+bar];
(%o4)                 [foo + bar, foo+bar]
(%i5) [1729, \1729];
(%o5)                     [1729, 1729]
(%i6) [symbolp (foo\+bar), symbolp (\1729)];
(%o6)                     [true, true]
(%i7) [is (foo\+bar = foo+bar), is (\1729 = 1729)];
(%o7)                    [false, false]
(%i8) baz\~quux;
(%o8)                       baz~quux
(%i9) declare ("~", alphabetic);
(%o9)                         done
(%i10) baz~quux;
(%o10)                      baz~quux
(%i11) [is (foo = FOO), is (FOO = Foo), is (Foo = foo)];
(%o11)                [false, false, false]
(%i12) :lisp (defvar *my-lisp-variable* '$foo)
*MY-LISP-VARIABLE*
(%i12) ?\*my\-lisp\-variable\*;
(%o12)                         foo

Categories:  Syntax


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6.4 Inequality

Maxima has the inequality operators <, <=, >=, >, #, and notequal. See if for a description of conditional expressions.


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6.5 Functions and Variables for Expressions

Function: alias (new_name_1, old_name_1, …, new_name_n, old_name_n)

provides an alternate name for a (user or system) function, variable, array, etc. Any even number of arguments may be used.

System variable: aliases

Default value: []

aliases is the list of atoms which have a user defined alias (set up by the alias, ordergreat, orderless functions or by declaring the atom a noun with declare. )

Keyword: allbut

works with the part commands (i.e. part, inpart, substpart, substinpart, dpart, and lpart ). For example,

(%i1) expr : e + d + c + b + a;
(%o1)                   e + d + c + b + a
(%i2) part (expr, [2, 5]);
(%o2)                         d + a

while

(%i1) expr : e + d + c + b + a;
(%o1)                   e + d + c + b + a
(%i2) part (expr, allbut (2, 5));
(%o2)                       e + c + b

allbut is also recognized by kill.

(%i1) [aa : 11, bb : 22, cc : 33, dd : 44, ee : 55];
(%o1)                 [11, 22, 33, 44, 55]
(%i2) kill (allbut (cc, dd));
(%o0)                         done
(%i1) [aa, bb, cc, dd];
(%o1)                   [aa, bb, 33, 44]

kill(allbut(a_1, a_2, ...)) has the effect of kill(all) except that it does not kill the symbols a_1, a_2, …

Function: args (expr)

Returns the list of arguments of expr, which may be any kind of expression other than an atom. Only the arguments of the top-level operator are extracted; subexpressions of expr appear as elements or subexpressions of elements of the list of arguments.

The order of the items in the list may depend on the global flag inflag.

args (expr) is equivalent to substpart ("[", expr, 0). See also substpart, and op.

Categories:  Expressions

Function: atom (expr)

Returns true if expr is atomic (i.e. a number, name or string) else false. Thus atom(5) is true while atom(a[1]) and atom(sin(x)) are false (assuming a[1] and x are unbound).

Categories:  Expressions · Predicate functions

Function: box (expr)
Function: box (expr, a)

Returns expr enclosed in a box. The return value is an expression with box as the operator and expr as the argument. A box is drawn on the display when display2d is true.

box (expr, a) encloses expr in a box labelled by the symbol a. The label is truncated if it is longer than the width of the box.

box evaluates its argument. However, a boxed expression does not evaluate to its content, so boxed expressions are effectively excluded from computations.

boxchar is the character used to draw the box in box and in the dpart and lpart functions.

Examples:

(%i1) box (a^2 + b^2);
                            """""""""
                            " 2    2"
(%o1)                       "b  + a "
                            """""""""
(%i2) a : 1234;
(%o2)                         1234
(%i3) b : c - d;
(%o3)                         c - d
(%i4) box (a^2 + b^2);
                      """"""""""""""""""""
                      "       2          "
(%o4)                 "(c - d)  + 1522756"
                      """"""""""""""""""""
(%i5) box (a^2 + b^2, term_1);
                      term_1""""""""""""""
                      "       2          "
(%o5)                 "(c - d)  + 1522756"
                      """"""""""""""""""""
(%i6) 1729 - box (1729);
                                 """"""
(%o6)                     1729 - "1729"
                                 """"""
(%i7) boxchar: "-";
(%o7)                           -
(%i8) box (sin(x) + cos(y));
                        -----------------
(%o8)                   -cos(y) + sin(x)-
                        -----------------

Categories:  Expressions

Option variable: boxchar

Default value: "

boxchar is the character used to draw the box in the box and in the dpart and lpart functions.

All boxes in an expression are drawn with the current value of boxchar; the drawing character is not stored with the box expression.

Categories:  Expressions

Function: collapse (expr)

Collapses expr by causing all of its common (i.e., equal) subexpressions to share (i.e., use the same cells), thereby saving space. (collapse is a subroutine used by the optimize command.) Thus, calling collapse may be useful after loading in a save file. You can collapse several expressions together by using collapse ([expr_1, ..., expr_n]). Similarly, you can collapse the elements of the array A by doing collapse (listarray ('A)).

Categories:  Expressions

Function: disolate (expr, x_1, …, x_n)

is similar to isolate (expr, x) except that it enables the user to isolate more than one variable simultaneously. This might be useful, for example, if one were attempting to change variables in a multiple integration, and that variable change involved two or more of the integration variables. This function is autoloaded from `simplification/disol.mac'. A demo is available by demo("disol")$.

Categories:  Expressions

Function: dispform (expr)
Function: dispform (expr, all)

Returns the external representation of expr.

dispform(expr) returns the external representation with respect to the main (top-level) operator. dispform(expr, all) returns the external representation with respect to all operators in expr.

See also part, inpart, and inflag.

Examples:

The internal representation of - x is "negative one times x" while the external representation is "minus x".

(%i1) - x;
(%o1)                          - x
(%i2) ?format (true, "~S~%", %);
((MTIMES SIMP) -1 $X)
(%o2)                         false
(%i3) dispform (- x);
(%o3)                          - x
(%i4) ?format (true, "~S~%", %);
((MMINUS SIMP) $X)
(%o4)                         false

The internal representation of sqrt(x) is "x to the power 1/2" while the external representation is "square root of x".

(%i1) sqrt (x);
(%o1)                        sqrt(x)
(%i2) ?format (true, "~S~%", %);
((MEXPT SIMP) $X ((RAT SIMP) 1 2))
(%o2)                         false
(%i3) dispform (sqrt (x));
(%o3)                        sqrt(x)
(%i4) ?format (true, "~S~%", %);
((%SQRT SIMP) $X)
(%o4)                         false

Use of the optional argument all.

(%i1) expr : sin (sqrt (x));
(%o1)                     sin(sqrt(x))
(%i2) freeof (sqrt, expr);
(%o2)                         true
(%i3) freeof (sqrt, dispform (expr));
(%o3)                         true
(%i4) freeof (sqrt, dispform (expr, all));
(%o4)                         false

Categories:  Expressions

Function: dpart (expr, n_1, …, n_k)

Selects the same subexpression as part, but instead of just returning that subexpression as its value, it returns the whole expression with the selected subexpression displayed inside a box. The box is actually part of the expression.

(%i1) dpart (x+y/z^2, 1, 2, 1);
                             y
(%o1)                       ---- + x
                               2
                            """
                            "z"
                            """

Categories:  Expressions

Option variable: exptisolate

Default value: false

exptisolate, when true, causes isolate (expr, var) to examine exponents of atoms (such as %e) which contain var.

Categories:  Expressions

Option variable: exptsubst

Default value: false

exptsubst, when true, permits substitutions such as y for %e^x in %e^(a x).

Function: freeof (x_1, …, x_n, expr)

freeof (x_1, expr) returns true if no subexpression of expr is equal to x_1 or if x_1 occurs only as a dummy variable in expr, or if x_1 is neither the noun nor verb form of any operator in expr, and returns false otherwise.

freeof (x_1, ..., x_n, expr) is equivalent to freeof (x_1, expr) and ... and freeof (x_n, expr).

The arguments x_1, …, x_n may be names of functions and variables, subscripted names, operators (enclosed in double quotes), or general expressions. freeof evaluates its arguments.

freeof operates only on expr as it stands (after simplification and evaluation) and does not attempt to determine if some equivalent expression would give a different result. In particular, simplification may yield an equivalent but different expression which comprises some different elements than the original form of expr.

A variable is a dummy variable in an expression if it has no binding outside of the expression. Dummy variables recognized by freeof are the index of a sum or product, the limit variable in limit, the integration variable in the definite integral form of integrate , the original variable in laplace, formal variables in at expressions, and arguments in lambda expressions.

The indefinite form of integrate is not free of its variable of integration.

Examples:

Arguments are names of functions, variables, subscripted names, operators, and expressions. freeof (a, b, expr) is equivalent to freeof (a, expr) and freeof (b, expr).

(%i1) expr: z^3 * cos (a[1]) * b^(c+d);
                                 d + c  3
(%o1)                   cos(a ) b      z
                             1
(%i2) freeof (z, expr);
(%o2)                         false
(%i3) freeof (cos, expr);
(%o3)                         false
(%i4) freeof (a[1], expr);
(%o4)                         false
(%i5) freeof (cos (a[1]), expr);
(%o5)                         false
(%i6) freeof (b^(c+d), expr);
(%o6)                         false
(%i7) freeof ("^", expr);
(%o7)                         false
(%i8) freeof (w, sin, a[2], sin (a[2]), b*(c+d), expr);
(%o8)                         true

freeof evaluates its arguments.

(%i1) expr: (a+b)^5$
(%i2) c: a$
(%i3) freeof (c, expr);
(%o3)                         false

freeof does not consider equivalent expressions. Simplification may yield an equivalent but different expression.

(%i1) expr: (a+b)^5$
(%i2) expand (expr);
          5        4       2  3       3  2      4      5
(%o2)    b  + 5 a b  + 10 a  b  + 10 a  b  + 5 a  b + a
(%i3) freeof (a+b, %);
(%o3)                         true
(%i4) freeof (a+b, expr);
(%o4)                         false
(%i5) exp (x);
                                 x
(%o5)                          %e
(%i6) freeof (exp, exp (x));
(%o6)                         true

A summation or definite integral is free of its dummy variable. An indefinite integral is not free of its variable of integration.

(%i1) freeof (i, 'sum (f(i), i, 0, n));
(%o1)                         true
(%i2) freeof (x, 'integrate (x^2, x, 0, 1));
(%o2)                         true
(%i3) freeof (x, 'integrate (x^2, x));
(%o3)                         false

Categories:  Expressions

Option variable: inflag

Default value: false

When inflag is true, functions for part extraction inspect the internal form of expr.

Note that the simplifier re-orders expressions. Thus first (x + y) returns x if inflag is true and y if inflag is false. (first (y + x) gives the same results.)

Also, setting inflag to true and calling part or substpart is the same as calling inpart or substinpart.

Functions affected by the setting of inflag are: part, substpart, first, rest, last, length, the forin construct, map, fullmap, maplist, reveal and pickapart.

Categories:  Expressions

Function: inpart (expr, n_1, …, n_k)

is similar to part but works on the internal representation of the expression rather than the displayed form and thus may be faster since no formatting is done. Care should be taken with respect to the order of subexpressions in sums and products (since the order of variables in the internal form is often different from that in the displayed form) and in dealing with unary minus, subtraction, and division (since these operators are removed from the expression). part (x+y, 0) or inpart (x+y, 0) yield +, though in order to refer to the operator it must be enclosed in "s. For example ... if inpart (%o9,0) = "+" then ....

Examples:

(%i1) x + y + w*z;
(%o1)                      w z + y + x
(%i2) inpart (%, 3, 2);
(%o2)                           z
(%i3) part (%th (2), 1, 2);
(%o3)                           z
(%i4) 'limit (f(x)^g(x+1), x, 0, minus);
                                  g(x + 1)
(%o4)                 limit   f(x)
                      x -> 0-
(%i5) inpart (%, 1, 2);
(%o5)                       g(x + 1)

Categories:  Expressions

Function: isolate (expr, x)

Returns expr with subexpressions which are sums and which do not contain var replaced by intermediate expression labels (these being atomic symbols like %t1, %t2, …). This is often useful to avoid unnecessary expansion of subexpressions which don't contain the variable of interest. Since the intermediate labels are bound to the subexpressions they can all be substituted back by evaluating the expression in which they occur.

exptisolate (default value: false) if true will cause isolate to examine exponents of atoms (like %e) which contain var.

isolate_wrt_times if true, then isolate will also isolate with respect to products. See isolate_wrt_times.

Do example (isolate) for examples.

Categories:  Expressions

Option variable: isolate_wrt_times

Default value: false

When isolate_wrt_times is true, isolate will also isolate with respect to products. E.g. compare both settings of the switch on

(%i1) isolate_wrt_times: true$
(%i2) isolate (expand ((a+b+c)^2), c);

(%t2)                          2 a


(%t3)                          2 b


                          2            2
(%t4)                    b  + 2 a b + a

                     2
(%o4)               c  + %t3 c + %t2 c + %t4
(%i4) isolate_wrt_times: false$
(%i5) isolate (expand ((a+b+c)^2), c);
                     2
(%o5)               c  + 2 b c + 2 a c + %t4

Categories:  Expressions

Option variable: listconstvars

Default value: false

When listconstvars is true, it will cause listofvars to include %e, %pi, %i, and any variables declared constant in the list it returns if they appear in the expression listofvars is called on. The default is to omit these.

Categories:  Expressions

Option variable: listdummyvars

Default value: true

When listdummyvars is false, "dummy variables" in the expression will not be included in the list returned by listofvars. (The meaning of "dummy variables" is as given in freeof. "Dummy variables" are mathematical things like the index of a sum or product, the limit variable, and the definite integration variable.)

Example:

(%i1) listdummyvars: true$
(%i2) listofvars ('sum(f(i), i, 0, n));
(%o2)                        [i, n]
(%i3) listdummyvars: false$
(%i4) listofvars ('sum(f(i), i, 0, n));
(%o4)                          [n]

Categories:  Expressions

Function: listofvars (expr)

Returns a list of the variables in expr.

listconstvars if true causes listofvars to include %e, %pi, %i, and any variables declared constant in the list it returns if they appear in expr. The default is to omit these.

See also the option variable listdummyvars to exclude or include "dummy variables" in the list of variables.

(%i1) listofvars (f (x[1]+y) / g^(2+a));
(%o1)                     [g, a, x , y]
                                  1

Categories:  Expressions

Function: lfreeof (list, expr)

For each member m of list, calls freeof (m, expr). It returns false if any call to freeof does and true otherwise.

Categories:  Expressions

Function: lpart (label, expr, n_1, …, n_k)

is similar to dpart but uses a labelled box. A labelled box is similar to the one produced by dpart but it has a name in the top line.

Categories:  Expressions

Property: mainvar

You may declare variables to be mainvar. The ordering scale for atoms is essentially: numbers < constants (e.g., %e, %pi) < scalars < other variables < mainvars. E.g., compare expand ((X+Y)^4) with (declare (x, mainvar), expand ((x+y)^4)). (Note: Care should be taken if you elect to use the above feature. E.g., if you subtract an expression in which x is a mainvar from one in which x isn't a mainvar, resimplification e.g. with ev (expr, simp) may be necessary if cancellation is to occur. Also, if you save an expression in which x is a mainvar, you probably should also save x.)

Property: noun

noun is one of the options of the declare command. It makes a function so declared a "noun", meaning that it won't be evaluated automatically.

Example:

(%i1) factor (12345678);
                             2
(%o1)                     2 3  47 14593
(%i2) declare (factor, noun);
(%o2)                         done
(%i3) factor (12345678);
(%o3)                   factor(12345678)
(%i4) ''%, nouns;
                             2
(%o4)                     2 3  47 14593

Categories:  Nouns and verbs

Option variable: noundisp

Default value: false

When noundisp is true, nouns display with a single quote. This switch is always true when displaying function definitions.

Function: nounify (f)

Returns the noun form of the function name f. This is needed if one wishes to refer to the name of a verb function as if it were a noun. Note that some verb functions will return their noun forms if they can't be evaluated for certain arguments. This is also the form returned if a function call is preceded by a quote.

See also verbify.

Categories:  Nouns and verbs

Function: nterms (expr)

Returns the number of terms that expr would have if it were fully expanded out and no cancellations or combination of terms occurred. Note that expressions like sin (expr), sqrt (expr), exp (expr), etc. count as just one term regardless of how many terms expr has (if it is a sum).

Categories:  Expressions

Function: op (expr)

Returns the main operator of the expression expr. op (expr) is equivalent to part (expr, 0).

op returns a string if the main operator is a built-in or user-defined prefix, binary or n-ary infix, postfix, matchfix, or nofix operator. Otherwise, if expr is a subscripted function expression, op returns the subscripted function; in this case the return value is not an atom. Otherwise, expr is an array function or ordinary function expression, and op returns a symbol.

op observes the value of the global flag inflag.

op evaluates it argument.

See also args.

Examples:

(%i1) stringdisp: true$
(%i2) op (a * b * c);
(%o2)                          "*"
(%i3) op (a * b + c);
(%o3)                          "+"
(%i4) op ('sin (a + b));
(%o4)                          sin
(%i5) op (a!);
(%o5)                          "!"
(%i6) op (-a);
(%o6)                          "-"
(%i7) op ([a, b, c]);
(%o7)                          "["
(%i8) op ('(if a > b then c else d));
(%o8)                         "if"
(%i9) op ('foo (a));
(%o9)                          foo
(%i10) prefix (foo);
(%o10)                        "foo"
(%i11) op (foo a);
(%o11)                        "foo"
(%i12) op (F [x, y] (a, b, c));
(%o12)                        F
                               x, y
(%i13) op (G [u, v, w]);
(%o13)                          G

Categories:  Expressions · Operators

Function: operatorp (expr, op)
Function: operatorp (expr, [op_1, …, op_n])

operatorp (expr, op) returns true if op is equal to the operator of expr.

operatorp (expr, [op_1, ..., op_n]) returns true if some element op_1, …, op_n is equal to the operator of expr.

Categories:  Operators · Predicate functions

Option variable: opsubst

Default value: true

When opsubst is false, subst does not attempt to substitute into the operator of an expression. E.g., (opsubst: false, subst (x^2, r, r+r[0])) will work.

Categories:  Expressions

Function: optimize (expr)

Returns an expression that produces the same value and side effects as expr but does so more efficiently by avoiding the recomputation of common subexpressions. optimize also has the side effect of "collapsing" its argument so that all common subexpressions are shared. Do example (optimize) for examples.

Categories:  Expressions

Option variable: optimprefix

Default value: %

optimprefix is the prefix used for generated symbols by the optimize command.

Categories:  Expressions

Function: ordergreat (v_1, …, v_n)
Function: orderless (v_1, …, v_n)

ordergreat changes the canonical ordering of Maxima expressions such that v_1 succeeds v_2 succeeds … succeeds v_n, and v_n succeeds any other symbol not mentioned as an argument.

orderless changes the canonical ordering of Maxima expressions such that v_1 precedes v_2 precedes … precedes v_n, and v_n precedes any other variable not mentioned as an argument.

The order established by ordergreat and orderless is dissolved by unorder. ordergreat and orderless can be called only once each, unless unorder is called; only the last call to ordergreat and orderless has any effect.

See also ordergreatp.

Categories:  Expressions

Function: ordergreatp (expr_1, expr_2)
Function: orderlessp (expr_1, expr_2)

ordergreatp returns true if expr_1 succeeds expr_2 in the canonical ordering of Maxima expressions, and false otherwise.

orderlessp returns true if expr_1 precedes expr_2 in the canonical ordering of Maxima expressions, and false otherwise.

All Maxima atoms and expressions are comparable under ordergreatp and orderlessp, although there are isolated examples of expressions for which these predicates are not transitive; that is a bug.

The canonical ordering of atoms (symbols, literal numbers, and strings) is the following.

(integers and floats) precede (bigfloats) precede (declared constants) precede (strings) precede (declared scalars) precede (first argument to orderless ) precedes … precedes (last argument to orderless) precedes (other symbols) precede (last argument to ordergreat ) precedes … precedes (first argument to ordergreat) precedes (declared main variables)

For non-atomic expressions, the canonical ordering is derived from the ordering for atoms. For the built-in + * and ^ operators, the ordering is not easily summarized. For other built-in operators and all other functions and operators, expressions are ordered by their arguments (beginning with the first argument), then by the name of the operator or function. In the case of subscripted expressions, the subscripted symbol is considered the operator and the subscript is considered an argument.

The canonical ordering of expressions is modified by the functions ordergreat and orderless, and the mainvar, constant, and scalar declarations.

See also sort.

Examples:

Ordering ordinary symbols and constants. Note that %pi is not ordered according to its numerical value.

(%i1) stringdisp : true;
(%o1)                         true
(%i2) sort([%pi, 3b0, 3.0, x, X, "foo", 3, a, 4, "bar", 4.0, 4b0]);
(%o2) [3, 3.0, 4, 4.0, 3.0b0, 4.0b0, %pi, "bar", "foo", a, x, X]

Effect of ordergreat and orderless functions.

(%i1) sort ([M, H, K, T, E, W, G, A, P, J, S]);
(%o1)           [A, E, G, H, J, K, M, P, S, T, W]
(%i2) ordergreat (S, J);
(%o2)                         done
(%i3) orderless (M, H);
(%o3)                         done
(%i4) sort ([M, H, K, T, E, W, G, A, P, J, S]);
(%o4)           [M, H, A, E, G, K, P, T, W, J, S]

Effect of mainvar, constant, and scalar declarations.

(%i1) sort ([aa, foo, bar, bb, baz, quux, cc, dd, A1, B1, C1]);
(%o1)   [aa, bar, baz, bb, cc, dd, foo, quux, A1, B1, C1]
(%i2) declare (aa, mainvar);
(%o2)                         done
(%i3) declare ([baz, quux], constant);
(%o3)                         done
(%i4) declare ([A1, B1], scalar);
(%o4)                         done
(%i5) sort ([aa, foo, bar, bb, baz, quux, cc, dd, A1, B1, C1]);
(%o5)   [baz, quux, A1, B1, bar, bb, cc, dd, foo, C1, aa]

Ordering non-atomic expressions.

(%i1) sort([1, 2, n, f(1), f(2), f(2, 1), g(1), g(1, 2), g(n),
            f(n, 1)]);
(%o1) [1, 2, f(1), g(1), g(1, 2), f(2), f(2, 1), n, g(n), 
                                                         f(n, 1)]
(%i2) sort ([foo(1), X[1], X[k], foo(k), 1, k]);
(%o2)            [1, foo(1), X , k, foo(k), X ]
                              1              k

Categories:  Expressions · Predicate functions

Function: part (expr, n_1, …, n_k)

Returns parts of the displayed form of expr. It obtains the part of expr as specified by the indices n_1, …, n_k. First part n_1 of expr is obtained, then part n_2 of that, etc. The result is part n_k of … part n_2 of part n_1 of expr. If no indices are specified expr is returned.

part can be used to obtain an element of a list, a row of a matrix, etc.

If the last argument to a part function is a list of indices then several subexpressions are picked out, each one corresponding to an index of the list. Thus part (x + y + z, [1, 3]) is z+x.

piece holds the last expression selected when using the part functions. It is set during the execution of the function and thus may be referred to in the function itself as shown below.

If partswitch is set to true then end is returned when a selected part of an expression doesn't exist, otherwise an error message is given.

See also inpart, substpart, substinpart, dpart, and lpart.

Examples:

(%i1) part(z+2*y+a,2);
(%o1)                                 2 y
(%i2) part(z+2*y+a,[1,3]);
(%o2)                                z + a
(%i3) part(z+2*y+a,2,1);
(%o3)                                  2

example (part) displays additional examples.

Categories:  Expressions

Function: partition (expr, x)

Returns a list of two expressions. They are (1) the factors of expr (if it is a product), the terms of expr (if it is a sum), or the list (if it is a list) which don't contain x and, (2) the factors, terms, or list which do.

Examples:

(%i1) partition (2*a*x*f(x), x);
(%o1)                     [2 a, x f(x)]
(%i2) partition (a+b, x);
(%o2)                      [b + a, 0]
(%i3) partition ([a, b, f(a), c], a); 
(%o3)                  [[b, c], [a, f(a)]]

Categories:  Expressions

Option variable: partswitch

Default value: false

When partswitch is true, end is returned when a selected part of an expression doesn't exist, otherwise an error message is given.

Categories:  Expressions

Function: pickapart (expr, n)

Assigns intermediate expression labels to subexpressions of expr at depth n, an integer. Subexpressions at greater or lesser depths are not assigned labels. pickapart returns an expression in terms of intermediate expressions equivalent to the original expression expr.

See also part, dpart, lpart, inpart, and reveal.

Examples:

(%i1) expr: (a+b)/2 + sin (x^2)/3 - log (1 + sqrt(x+1));
                                          2
                                     sin(x )   b + a
(%o1)       - log(sqrt(x + 1) + 1) + ------- + -----
                                        3        2
(%i2) pickapart (expr, 0);
                                          2
                                     sin(x )   b + a
(%t2)       - log(sqrt(x + 1) + 1) + ------- + -----
                                        3        2
(%o2)                          %t2
(%i3) pickapart (expr, 1);

(%t3)                - log(sqrt(x + 1) + 1)


                                  2
                             sin(x )
(%t4)                        -------
                                3


                              b + a
(%t5)                         -----
                                2

(%o5)                    %t5 + %t4 + %t3
(%i5) pickapart (expr, 2);

(%t6)                 log(sqrt(x + 1) + 1)


                                  2
(%t7)                        sin(x )


(%t8)                         b + a

                         %t8   %t7
(%o8)                    --- + --- - %t6
                          2     3
(%i8) pickapart (expr, 3);

(%t9)                    sqrt(x + 1) + 1


                                2
(%t10)                         x

                  b + a              sin(%t10)
(%o10)            ----- - log(%t9) + ---------
                    2                    3
(%i10) pickapart (expr, 4);

(%t11)                     sqrt(x + 1)
                      2
                 sin(x )   b + a
(%o11)           ------- + ----- - log(%t11 + 1)
                    3        2
(%i11) pickapart (expr, 5);

(%t12)                        x + 1

                   2
              sin(x )   b + a
(%o12)        ------- + ----- - log(sqrt(%t12) + 1)
                 3        2
(%i12) pickapart (expr, 6);
                  2
             sin(x )   b + a
(%o12)       ------- + ----- - log(sqrt(x + 1) + 1)
                3        2

Categories:  Expressions

System variable: piece

Holds the last expression selected when using the part functions. It is set during the execution of the function and thus may be referred to in the function itself.

Categories:  Expressions

Function: psubst (list, expr)
Function: psubst (a, b, expr)

psubst(a, b, expr) is simliar to subst. See subst.

In distinction from subst the function psubst makes parallel substitutions, if the first argument list is a list of equations.

See also sublis for making parallel substitutions.

Example:

The first example shows parallel substitution with psubst. The second example shows the result for the function subst, which does a serial substitution.

(%i4) psubst ([a^2=b, b=a], sin(a^2) + sin(b));
(%o4)                           sin(b) + sin(a)
(%i5) subst ([a^2=b, b=a], sin(a^2) + sin(b));
(%o5)                              2 sin(a)

Categories:  Expressions

Function: rembox (expr, unlabelled)
Function: rembox (expr, label)
Function: rembox (expr)

Removes boxes from expr.

rembox (expr, unlabelled) removes all unlabelled boxes from expr.

rembox (expr, label) removes only boxes bearing label.

rembox (expr) removes all boxes, labelled and unlabelled.

Boxes are drawn by the box, dpart, and lpart functions.

Examples:

(%i1) expr: (a*d - b*c)/h^2 + sin(%pi*x);
                                  a d - b c
(%o1)                sin(%pi x) + ---------
                                      2
                                     h
(%i2) dpart (dpart (expr, 1, 1), 2, 2);
                        """""""    a d - b c
(%o2)               sin("%pi x") + ---------
                        """""""      """"
                                     " 2"
                                     "h "
                                     """"
(%i3) expr2: lpart (BAR, lpart (FOO, %, 1), 2);
                  FOO"""""""""""   BAR""""""""
                  "    """"""" "   "a d - b c"
(%o3)             "sin("%pi x")" + "---------"
                  "    """"""" "   "  """"   "
                  """"""""""""""   "  " 2"   "
                                   "  "h "   "
                                   "  """"   "
                                   """""""""""
(%i4) rembox (expr2, unlabelled);
                                  BAR""""""""
                   FOO"""""""""   "a d - b c"
(%o4)              "sin(%pi x)" + "---------"
                   """"""""""""   "    2    "
                                  "   h     "
                                  """""""""""
(%i5) rembox (expr2, FOO);
                                  BAR""""""""
                       """""""    "a d - b c"
(%o5)              sin("%pi x") + "---------"
                       """""""    "  """"   "
                                  "  " 2"   "
                                  "  "h "   "
                                  "  """"   "
                                  """""""""""
(%i6) rembox (expr2, BAR);
                   FOO"""""""""""
                   "    """"""" "   a d - b c
(%o6)              "sin("%pi x")" + ---------
                   "    """"""" "     """"
                   """"""""""""""     " 2"
                                      "h "
                                      """"
(%i7) rembox (expr2);
                                  a d - b c
(%o7)                sin(%pi x) + ---------
                                      2
                                     h

Categories:  Expressions

Function: reveal (expr, depth)

Replaces parts of expr at the specified integer depth with descriptive summaries.

When depth is greater than or equal to the maximum depth of expr, reveal (expr, depth) returns expr unmodified.

reveal evaluates its arguments. reveal returns the summarized expression.

Example:

(%i1) e: expand ((a - b)^2)/expand ((exp(a) + exp(b))^2);
                          2            2
                         b  - 2 a b + a
(%o1)               -------------------------
                        b + a     2 b     2 a
                    2 %e      + %e    + %e
(%i2) reveal (e, 1);
(%o2)                       Quotient
(%i3) reveal (e, 2);
                             Sum(3)
(%o3)                        ------
                             Sum(3)
(%i4) reveal (e, 3);
                     Expt + Negterm + Expt
(%o4)               ------------------------
                    Product(2) + Expt + Expt
(%i5) reveal (e, 4);
                       2                 2
                      b  - Product(3) + a
(%o5)         ------------------------------------
                         Product(2)     Product(2)
              2 Expt + %e           + %e
(%i6) reveal (e, 5);
                         2            2
                        b  - 2 a b + a
(%o6)              --------------------------
                       Sum(2)     2 b     2 a
                   2 %e       + %e    + %e
(%i7) reveal (e, 6);
                          2            2
                         b  - 2 a b + a
(%o7)               -------------------------
                        b + a     2 b     2 a
                    2 %e      + %e    + %e

Categories:  Expressions · Display functions

Function: sublis (list, expr)

Makes multiple parallel substitutions into an expression. list is a list of equations. The left hand side of the equations must be an atom.

The variable sublis_apply_lambda controls simplification after sublis.

See also psubst for making parallel substitutions.

Example:

(%i1) sublis ([a=b, b=a], sin(a) + cos(b));
(%o1)                    sin(b) + cos(a)

Categories:  Expressions

Option variable: sublis_apply_lambda

Default value: true

Controls whether lambda's substituted are applied in simplification after sublis is used or whether you have to do an ev to get things to apply. true means do the application.

Categories:  Expressions

Option variable: subnumsimp

Default value: false

If true then the functions subst and psubst can substitute a subscripted variable f[x] with a number, when only the symbol f is given.

See also subst.

(%i1) subst(100,g,g[x]+2);

subst: cannot substitute 100 for operator g in expression g
                                                           x
 -- an error. To debug this try: debugmode(true);

(%i2) subst(100,g,g[x]+2),subnumsimp:true;
(%o2)                          102

Categories:  Expressions

Function: subst (a, b, c)

Substitutes a for b in c. b must be an atom or a complete subexpression of c. For example, x+y+z is a complete subexpression of 2*(x+y+z)/w while x+y is not. When b does not have these characteristics, one may sometimes use substpart or ratsubst (see below). Alternatively, if b is of the form e/f then one could use subst (a*f, e, c) while if b is of the form e^(1/f) then one could use subst (a^f, e, c). The subst command also discerns the x^y in x^-y so that subst (a, sqrt(x), 1/sqrt(x)) yields 1/a. a and b may also be operators of an expression enclosed in double-quotes " or they may be function names. If one wishes to substitute for the independent variable in derivative forms then the at function (see below) should be used.

subst is an alias for substitute.

The commands subst (eq_1, expr) or subst ([eq_1, ..., eq_k], expr) are other permissible forms. The eq_i are equations indicating substitutions to be made. For each equation, the right side will be substituted for the left in the expression expr. The equations are substituted in serial from left to right in expr. See the functions sublis and psubst for making parallel substitutions.

exptsubst if true permits substitutions like y for %e^x in %e^(a*x) to take place.

When opsubst is false, subst will not attempt to substitute into the operator of an expression. E.g. (opsubst: false, subst (x^2, r, r+r[0])) will work.

Examples:

(%i1) subst (a, x+y, x + (x+y)^2 + y);
                                    2
(%o1)                      y + x + a
(%i2) subst (-%i, %i, a + b*%i);
(%o2)                       a - %i b

The substitution is done in serial for a list of equations. Compare this with a parallel substitution:

(%i3) subst([a=b, b=c], a+b);
(%o3)                                 2 c
(%i4) sublis([a=b, b=c], a+b);
(%o4)                                c + b

For further examples, do example (subst).

Categories:  Expressions

Function: substinpart (x, expr, n_1, …, n_k)

Similar to substpart, but substinpart works on the internal representation of expr.

Examples:

(%i1) x . 'diff (f(x), x, 2);
                              2
                             d
(%o1)                   x . (--- (f(x)))
                               2
                             dx
(%i2) substinpart (d^2, %, 2);
                                  2
(%o2)                        x . d
(%i3) substinpart (f1, f[1](x + 1), 0);
(%o3)                       f1(x + 1)

If the last argument to a part function is a list of indices then several subexpressions are picked out, each one corresponding to an index of the list. Thus

(%i1) part (x + y + z, [1, 3]);
(%o1)                         z + x

piece holds the value of the last expression selected when using the part functions. It is set during the execution of the function and thus may be referred to in the function itself as shown below. If partswitch is set to true then end is returned when a selected part of an expression doesn't exist, otherwise an error message is given.

(%i1) expr: 27*y^3 + 54*x*y^2 + 36*x^2*y + y + 8*x^3 + x + 1;
              3         2       2            3
(%o1)     27 y  + 54 x y  + 36 x  y + y + 8 x  + x + 1
(%i2) part (expr, 2, [1, 3]);
                                  2
(%o2)                         54 y
(%i3) sqrt (piece/54);
(%o3)                        abs(y)
(%i4) substpart (factor (piece), expr, [1, 2, 3, 5]);
                               3
(%o4)               (3 y + 2 x)  + y + x + 1
(%i5) expr: 1/x + y/x - 1/z;
                             1   y   1
(%o5)                      - - + - + -
                             z   x   x
(%i6) substpart (xthru (piece), expr, [2, 3]);
                            y + 1   1
(%o6)                       ----- - -
                              x     z

Also, setting the option inflag to true and calling part

or substpart is the same as calling inpart or substinpart.

Categories:  Expressions

Function: substpart (x, expr, n_1, …, n_k)

Substitutes x for the subexpression picked out by the rest of the arguments as in part. It returns the new value of expr. x may be some operator to be substituted for an operator of expr. In some cases x needs to be enclosed in double-quotes " (e.g. substpart ("+", a*b, 0) yields b + a).

Example:

(%i1) 1/(x^2 + 2);
                               1
(%o1)                        ------
                              2
                             x  + 2
(%i2) substpart (3/2, %, 2, 1, 2);
                               1
(%o2)                       --------
                             3/2
                            x    + 2
(%i3) a*x + f(b, y);
(%o3)                     a x + f(b, y)
(%i4) substpart ("+", %, 1, 0);
(%o4)                    x + f(b, y) + a

Also, setting the option inflag to true and calling part

or substpart is the same as calling inpart or substinpart.

Categories:  Expressions

Function: symbolp (expr)

Returns true if expr is a symbol, else false. In effect, symbolp(x) is equivalent to the predicate atom(x) and not numberp(x).

See also Identifiers.

Categories:  Predicate functions

Function: unorder ()

Disables the aliasing created by the last use of the ordering commands ordergreat and orderless. ordergreat and orderless may not be used more than one time each without calling unorder. unorder does not substitute back in expressions the original symbols for the aliases introduced by ordergreat and orderless. Therefore, after execution of unorder the aliases appear in previous expressions.

See also ordergreat and orderless.

Examples:

ordergreat(a) introduces an alias for the symbol a. Therefore, the difference of %o2 and %o4 does not vanish. unorder does not substitute back the symbol a and the alias appears in the output %o7.

(%i1) unorder();
(%o1)                          []
(%i2) b*x+a^2;
                                   2
(%o2)                       b x + a
(%i3) ordergreat(a);
(%o3)                         done
(%i4) b*x+a^2;
                             2
(%o4)                       a  + b x
(%i5) %th(1)-%th(3);
                              2    2
(%o5)                        a  - a
(%i6) unorder();
(%o6)                          [a]
(%i7) %th(2);
                                2    2
(%o7)                      _101a  - a

Categories:  Expressions

Function: verbify (f)

Returns the verb form of the function name f. See also verb, noun, and nounify.

Examples:

(%i1) verbify ('foo);
(%o1)                          foo
(%i2) :lisp $%
$FOO
(%i2) nounify (foo);
(%o2)                          foo
(%i3) :lisp $%
%FOO

Categories:  Nouns and verbs


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