Maxima 5.41.0 Manual: 11. Maximas Database

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# 11. Maximas Database

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## 11.1 Introduction to Maximas Database

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## 11.2 Functions and Variables for Properties

Property: alphabetic

  `alphabetic` is a property type recognized by `declare`. The expression `declare(s, alphabetic)` tells Maxima to recognize as alphabetic all of the characters in s, which must be a string.

  See also Identifiers.

  Example:

      (%i1) xx\~yy\`\@ : 1729;
      (%o1)                         1729
      (%i2) declare ("~`@", alphabetic);
      (%o2)                         done
      (%i3) xx~yy`@ + @yy`xx + `xx@@yy~;
      (%o3)               `xx@@yy~ + @yy`xx + 1729
      (%i4) listofvars (%);
      (%o4)                  [@yy`xx, `xx@@yy~]

  ·

  @ref{Category: Declarations and inferences}

Property: bindtest

  The command `declare(x, bindtest)` tells Maxima to trigger an error when the symbol x is evaluated unbound.

      (%i1) aa + bb;
      (%o1)                        bb + aa
      (%i2) declare (aa, bindtest);
      (%o2)                         done
      (%i3) aa + bb;
      aa unbound variable
       -- an error.  Quitting.  To debug this try debugmode(true);
      (%i4) aa : 1234;
      (%o4)                         1234
      (%i5) aa + bb;
      (%o5)                       bb + 1234

Property: constant

  `declare(a, constant)` declares a to be a constant. The declaration of a symbol to be constant does not prevent the assignment of a nonconstant value to the symbol.

  See `constantp` and `declare`.

  Example:

      (%i1) declare(c, constant);
      (%o1)                         done
      (%i2) constantp(c);
      (%o2)                         true
      (%i3) c : x;
      (%o3)                           x
      (%i4) constantp(c);
      (%o4)                         false

  ·

  @ref{Category: Declarations and inferences} · @ref{Category: Constants}

Function: constantp (expr)

  Returns `true` if expr is a constant expression, otherwise returns `false`.

  An expression is considered a constant expression if its arguments are numbers (including rational numbers, as displayed with `/R/`), symbolic constants such as `%pi`, `%e`, and `%i`, variables bound to a constant or declared constant by `declare`, or functions whose arguments are constant.

  `constantp` evaluates its arguments.

  See the property `constant` which declares a symbol to be constant.

  Examples:

      (%i1) constantp (7 * sin(2));
      (%o1)                                true
      (%i2) constantp (rat (17/29));
      (%o2)                                true
      (%i3) constantp (%pi * sin(%e));
      (%o3)                                true
      (%i4) constantp (exp (x));
      (%o4)                                false
      (%i5) declare (x, constant);
      (%o5)                                done
      (%i6) constantp (exp (x));
      (%o6)                                true
      (%i7) constantp (foo (x) + bar (%e) + baz (2));
      (%o7)                                false
      (%i8)

  ·

  @ref{Category: Predicate functions} · @ref{Category: Constants}

Function: declare (a_1, p_1, a_2, p_2, …)

  Assigns the atom or list of atoms a_i the property or list of properties p_i. When a_i and/or p_i are lists, each of the atoms gets all of the properties.

  `declare` quotes its arguments. `declare` always returns `done`.

  As noted in the description for each declaration flag, for some flags `featurep(object, feature)` returns `true` if object has been declared to have feature.

  For more information about the features system, see `features`. To remove a property from an atom, use `remove`.

  `declare` recognizes the following properties:

  `additive`

    Tells Maxima to simplify a_i expressions by the substitution `a_i(x + y + z + ...)` `-->` `a_i(x) + a_i(y) + a_i(z) + ...`. The substitution is carried out on the first argument only.

  `alphabetic`

    Tells Maxima to recognize all characters in a_i (which must be a string) as alphabetic characters.

  `antisymmetric, commutative, symmetric`

    Tells Maxima to recognize a_i as a symmetric or antisymmetric function. `commutative` is the same as `symmetric`.

  `bindtest`

    Tells Maxima to trigger an error when a_i is evaluated unbound.

  `constant`

    Tells Maxima to consider a_i a symbolic constant.

  `even, odd`

    Tells Maxima to recognize a_i as an even or odd integer variable.

  `evenfun, oddfun`

    Tells Maxima to recognize a_i as an odd or even function.

  `evflag`

    Makes a_i known to the `ev` function so that a_i is bound to `true` during the execution of `ev` when a_i appears as a flag argument of `ev`. See `evflag`.

  `evfun`

    Makes a_i known to `ev` so that the function named by a_i is applied when a_i appears as a flag argument of `ev`. See `evfun`.

  `feature`

    Tells Maxima to recognize a_i as the name of a feature. Other atoms may then be declared to have the a_i property.

  `increasing, decreasing`

    Tells Maxima to recognize a_i as an increasing or decreasing function.

  `integer, noninteger`

    Tells Maxima to recognize a_i as an integer or noninteger variable.

  `integervalued`

    Tells Maxima to recognize a_i as an integer-valued function.

  `lassociative, rassociative`

    Tells Maxima to recognize a_i as a right-associative or left-associative function.

  `linear`

    Equivalent to declaring a_i both `outative` and `additive`.

  `mainvar`

    Tells Maxima to consider a_i a "main variable". A main variable succeeds all other constants and variables in the canonical ordering of Maxima expressions, as determined by `ordergreatp`.

  `multiplicative`

    Tells Maxima to simplify a_i expressions by the substitution `a_i(x * y * z * ...)` `-->` `a_i(x) * a_i(y) * a_i(z) * ...`. The substitution is carried out on the first argument only.

  `nary`

    Tells Maxima to recognize a_i as an n-ary function.

    The `nary` declaration is not the same as calling the `nary` function. The sole effect of `declare(foo, nary)` is to instruct the Maxima simplifier to flatten nested expressions, for example, to simplify `foo(x, foo(y, z))` to `foo(x, y, z)`.

  `nonarray`

    Tells Maxima to consider a_i not an array. This declaration prevents multiple evaluation of a subscripted variable name.

  `nonscalar`

    Tells Maxima to consider a_i a nonscalar variable. The usual application is to declare a variable as a symbolic vector or matrix.

  `noun`

    Tells Maxima to parse a_i as a noun. The effect of this is to replace instances of a_i with `'a_i` or `nounify(a_i)`, depending on the context.

  `outative`

    Tells Maxima to simplify a_i expressions by pulling constant factors out of the first argument.

    When a_i has one argument, a factor is considered constant if it is a literal or declared constant.

    When a_i has two or more arguments, a factor is considered constant if the second argument is a symbol and the factor is free of the second argument.

  `posfun`

    Tells Maxima to recognize a_i as a positive function.

  `rational, irrational`

    Tells Maxima to recognize a_i as a rational or irrational real variable.

  `real, imaginary, complex`

    Tells Maxima to recognize a_i as a real, pure imaginary, or complex variable.

  `scalar`

    Tells Maxima to consider a_i a scalar variable.

  Examples of the usage of the properties are available in the documentation for each separate description of a property.

  ·

  @ref{Category: Declarations and inferences}

Property: decreasing
Property: increasing

  The commands `declare(f, decreasing)` or `declare(f, increasing)` tell Maxima to recognize the function f as an decreasing or increasing function.

  See also `declare` for more properties.

  Example:

      (%i1) assume(a > b);
      (%o1)                        [a > b]
      (%i2) is(f(a) > f(b));
      (%o2)                        unknown
      (%i3) declare(f, increasing);
      (%o3)                         done
      (%i4) is(f(a) > f(b));
      (%o4)                         true

  ·

  @ref{Category: Declarations and inferences}

Property: even
Property: odd

  `declare(a, even)` or `declare(a, odd)` tells Maxima to recognize the symbol a as an even or odd integer variable. The properties `even` and `odd` are not recognized by the functions `evenp`, `oddp`, and `integerp`.

  See also `declare` and `askinteger`.

  Example:

      (%i1) declare(n, even);
      (%o1)                         done
      (%i2) askinteger(n, even);
      (%o2)                          yes
      (%i3) askinteger(n);
      (%o3)                          yes
      (%i4) evenp(n);
      (%o4)                         false

  ·

  @ref{Category: Declarations and inferences}

Property: feature

  Maxima understands two distinct types of features, system features and features which apply to mathematical expressions. See also `status` for information about system features. See also `features` and `featurep` for information about mathematical features.

  `feature` itself is not the name of a function or variable.

Function: featurep (a, f)

  Attempts to determine whether the object a has the feature f on the basis of the facts in the current database. If so, it returns `true`, else `false`.

  Note that `featurep` returns `false` when neither f nor the negation of f can be established.

  `featurep` evaluates its argument.

  See also `declare` and `features`.

      (%i1) declare (j, even)$
      (%i2) featurep (j, integer);
      (%o2)                           true

  ·

  @ref{Category: Predicate functions} · @ref{Category: Declarations and inferences}

Declaration: features

  Maxima recognizes certain mathematical properties of functions and variables. These are called "features".

  `declare (x, foo)` gives the property foo to the function or variable x.

  `declare (foo, feature)` declares a new feature foo. For example, `declare ([red, green, blue], feature)` declares three new features, `red`, `green`, and `blue`.

  The predicate `featurep (x, foo)` returns `true` if x has the foo property, and `false` otherwise.

  The infolist `features` is a list of known features. These are

         integer        noninteger      even
         odd            rational        irrational
         real           imaginary       complex
         analytic       increasing      decreasing
         oddfun         evenfun         posfun
         constant       commutative     lassociative
         rassociative   symmetric       antisymmetric
         integervalued

  plus any user-defined features.

  `features` is a list of mathematical features. There is also a list of non-mathematical, system-dependent features. See `status`.

  Example:

      (%i1) declare (FOO, feature);
      (%o1)                         done
      (%i2) declare (x, FOO);
      (%o2)                         done
      (%i3) featurep (x, FOO);
      (%o3)                         true

  ·

  @ref{Category: Declarations and inferences}

Function: get (a, i)

  Retrieves the user property indicated by i associated with atom a or returns `false` if a doesn't have property i.

  `get` evaluates its arguments.

  See also `put` and `qput`.

      (%i1) put (%e, 'transcendental, 'type);
      (%o1)                    transcendental
      (%i2) put (%pi, 'transcendental, 'type)$
      (%i3) put (%i, 'algebraic, 'type)$
      (%i4) typeof (expr) := block ([q],
              if numberp (expr)
              then return ('algebraic),
              if not atom (expr)
              then return (maplist ('typeof, expr)),
              q: get (expr, 'type),
              if q=false
              then errcatch (error(expr,"is not numeric.")) else q)$
      (%i5) typeof (2*%e + x*%pi);
      x is not numeric.
      (%o5)  [[transcendental, []], [algebraic, transcendental]]
      (%i6) typeof (2*%e + %pi);
      (%o6)     [transcendental, [algebraic, transcendental]]

  ·

  @ref{Category: Declarations and inferences}

Property: integer
Property: noninteger

  `declare(a, integer)` or `declare(a, noninteger)` tells Maxima to recognize a as an integer or noninteger variable.

  See also `declare`.

  Example:

      (%i1) declare(n, integer, x, noninteger);
      (%o1)                         done
      (%i2) askinteger(n);
      (%o2)                          yes
      (%i3) askinteger(x);
      (%o3)                          no

  ·

  @ref{Category: Declarations and inferences}

Property: integervalued

  `declare(f, integervalued)` tells Maxima to recognize f as an integer-valued function.

  See also `declare`.

  Example:

      (%i1) exp(%i)^f(x);
                                    %i f(x)
      (%o1)                      (%e  )
      (%i2) declare(f, integervalued);
      (%o2)                         done
      (%i3) exp(%i)^f(x);
                                    %i f(x)
      (%o3)                       %e

  ·

  @ref{Category: Declarations and inferences}

Property: nonarray

  The command `declare(a, nonarray)` tells Maxima to consider a not an array. This declaration prevents multiple evaluation, if a is a subscripted variable.

  See also `declare`.

  Example:

      (%i1) a:'b$ b:'c$ c:'d$

      (%i4) a[x];
      (%o4)                          d
                                      x
      (%i5) declare(a, nonarray);
      (%o5)                         done
      (%i6) a[x];
      (%o6)                          a
                                      x

  ·

  @ref{Category: Expressions}

Property: nonscalar

  Makes atoms behave as does a list or matrix with respect to the dot operator.

  See also `declare`.

  ·

  @ref{Category: Declarations and inferences} · @ref{Category: Vectors} · @ref{Category: Matrices}

Function: nonscalarp (expr)

  Returns `true` if expr is a non-scalar, i.e., it contains atoms declared as non-scalars, lists, or matrices.

  See also the predicate function `scalarp` and `declare`.

  ·

  @ref{Category: Predicate functions} · @ref{Category: Vectors} · @ref{Category: Matrices}

Property: posfun

  `declare (f, posfun)` declares `f` to be a positive function. `is (f(x) > 0)` yields `true`.

  See also `declare`.

  ·

  @ref{Category: Declarations and inferences} · @ref{Category: Operators}

Function: printprops
`printprops` (a, i)
`printprops` ([a_1, …, a_n], i)
`printprops` (all, i)

  Displays the property with the indicator i associated with the atom a. a may also be a list of atoms or the atom `all` in which case all of the atoms with the given property will be used. For example, `printprops ([f, g], atvalue)`. `printprops` is for properties that cannot otherwise be displayed, i.e. for `atvalue`, `atomgrad`, `gradef`, and `matchdeclare`.

  ·

  @ref{Category: Declarations and inferences} · @ref{Category: Display functions}

Function: properties (a)

  Returns a list of the names of all the properties associated with the atom a.

  ·

  @ref{Category: Declarations and inferences}

System variable: props

  Default value: `[]`

  `props` are atoms which have any property other than those explicitly mentioned in `infolists`, such as specified by `atvalue`, `matchdeclare`, etc., as well as properties specified in the `declare` function.

  ·

  @ref{Category: Declarations and inferences} · @ref{Category: Global variables}

Function: propvars (prop)

  Returns a list of those atoms on the `props` list which have the property indicated by prop. Thus `propvars (atvalue)` returns a list of atoms which have atvalues.

  ·

  @ref{Category: Declarations and inferences}

Function: put (atom, value, indicator)

  Assigns value to the property (specified by indicator) of atom. indicator may be the name of any property, not just a system-defined property.

  `rem` reverses the effect of `put`.

  `put` evaluates its arguments. `put` returns value.

  See also `qput` and `get`.

  Examples:

      (%i1) put (foo, (a+b)^5, expr);
                                         5
      (%o1)                       (b + a)
      (%i2) put (foo, "Hello", str);
      (%o2)                         Hello
      (%i3) properties (foo);
      (%o3)            [[user properties, str, expr]]
      (%i4) get (foo, expr);
                                         5
      (%o4)                       (b + a)
      (%i5) get (foo, str);
      (%o5)                         Hello

  ·

  @ref{Category: Declarations and inferences}

Function: qput (atom, value, indicator)

  Assigns value to the property (specified by indicator) of atom. This is the same as `put`, except that the arguments are quoted.

  See also `get`.

  Example:

      (%i1) foo: aa$
      (%i2) bar: bb$
      (%i3) baz: cc$
      (%i4) put (foo, bar, baz);
      (%o4)                          bb
      (%i5) properties (aa);
      (%o5)                [[user properties, cc]]
      (%i6) get (aa, cc);
      (%o6)                          bb
      (%i7) qput (foo, bar, baz);
      (%o7)                          bar
      (%i8) properties (foo);
      (%o8)            [value, [user properties, baz]]
      (%i9) get ('foo, 'baz);
      (%o9)                          bar

  ·

  @ref{Category: Declarations and inferences}

Property: rational
Property: irrational

  `declare(a, rational)` or `declare(a, irrational)` tells Maxima to recognize a as a rational or irrational real variable.

  See also `declare`.

  ·

  @ref{Category: Declarations and inferences}

Property: real
Property: imaginary
Property: complex

  `declare(a, real)`, `declare(a, imaginary)`, or `declare(a, complex)` tells Maxima to recognize a as a real, pure imaginary, or complex variable.

  See also `declare`.

  ·

  @ref{Category: Declarations and inferences}

Function: rem (atom, indicator)

  Removes the property indicated by indicator from atom. `rem` reverses the effect of `put`.

  `rem` returns `done` if atom had an indicator property when `rem` was called, or `false` if it had no such property.

  ·

  @ref{Category: Declarations and inferences}

Function: remove
`remove` (a_1, p_1, …, a_n, p_n)
`remove` ([a_1, …, a_m], [p_1, …, p_n], …)
`remove` ("a", operator)
`remove` (a, transfun)
`remove` (all, p)

  Removes properties associated with atoms.

  `remove (a_1, p_1, ..., a_n, p_n)` removes property `p_k` from atom `a_k`.

  `remove ([a_1, ..., a_m], [p_1, ..., p_n], ...)` removes properties `p_1, ..., p_n` from atoms a_1, …, a_m. There may be more than one pair of lists.

  `remove (all, p)` removes the property p from all atoms which have it.

  The removed properties may be system-defined properties such as `function`, `macro`, or `mode_declare`. `remove` does not remove properties defined by `put`.

  A property may be `transfun` to remove the translated Lisp version of a function. After executing this, the Maxima version of the function is executed rather than the translated version.

  `remove ("a", operator)` or, equivalently, `remove ("a", op)` removes from a the operator properties declared by `prefix`, `infix`, `nary`, `postfix`, `matchfix`, or `nofix`. Note that the name of the operator must be written as a quoted string.

  `remove` always returns `done` whether or not an atom has a specified property. This behavior is unlike the more specific remove functions `remvalue`, `remarray`, `remfunction`, and `remrule`.

  `remove` quotes its arguments.

  ·

  @ref{Category: Declarations and inferences}

Property: scalar

  `declare(a, scalar)` tells Maxima to consider a a scalar variable.

  See also `declare`.

  ·

  @ref{Category: Declarations and inferences}

Function: scalarp (expr)

  Returns `true` if expr is a number, constant, or variable declared `scalar` with `declare`, or composed entirely of numbers, constants, and such variables, but not containing matrices or lists.

  See also the predicate function `nonscalarp`.

  ·

  @ref{Category: Predicate functions} · @ref{Category: Vectors} · @ref{Category: Matrices}

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## 11.3 Functions and Variables for Facts

Function: activate (context_1, …, context_n)

  Activates the contexts context_1, …, context_n. The facts in these contexts are then available to make deductions and retrieve information. The facts in these contexts are not listed by `facts ()`.

  The variable `activecontexts` is the list of contexts which are active by way of the `activate` function.

  ·

  @ref{Category: Declarations and inferences}

System variable: activecontexts

  Default value: `[]`

  `activecontexts` is a list of the contexts which are active by way of the `activate` function, as opposed to being active because they are subcontexts of the current context.

  ·

  @ref{Category: Declarations and inferences}

Function: askinteger
`askinteger` (expr, integer)
`askinteger` (expr)
`askinteger` (expr, even)
`askinteger` (expr, odd)

  `askinteger (expr, integer)` attempts to determine from the `assume` database whether expr is an integer. `askinteger` prompts the user if it cannot tell otherwise, and attempt to install the information in the database if possible. `askinteger (expr)` is equivalent to `askinteger (expr, integer)`.

  `askinteger (expr, even)` and `askinteger (expr, odd)` likewise attempt to determine if expr is an even integer or odd integer, respectively.

  ·

  @ref{Category: Declarations and inferences}

Function: asksign (expr)

  First attempts to determine whether the specified expression is positive, negative, or zero. If it cannot, it asks the user the necessary questions to complete its deduction. The user's answer is recorded in the data base for the duration of the current computation. The return value of `asksign` is one of `pos`, `neg`, or `zero`.

  ·

  @ref{Category: Declarations and inferences}

Function: assume (pred_1, …, pred_n)

  Adds predicates pred_1, …, pred_n to the current context. If a predicate is inconsistent or redundant with the predicates in the current context, it is not added to the context. The context accumulates predicates from each call to `assume`.

  `assume` returns a list whose elements are the predicates added to the context or the atoms `redundant` or `inconsistent` where applicable.

  The predicates pred_1, …, pred_n can only be expressions with the relational operators `< <= equal notequal >=` and `>`. Predicates cannot be literal equality `=` or literal inequality `#` expressions, nor can they be predicate functions such as `integerp`.

  Compound predicates of the form `pred_1 and ... and pred_n` are recognized, but not `pred_1 or ... or pred_n`. `not pred_k` is recognized if pred_k is a relational predicate. Expressions of the form `not (pred_1 and pred_2)` and `not (pred_1 or pred_2)` are not recognized.

  Maxima's deduction mechanism is not very strong; there are many obvious consequences which cannot be determined by `is`. This is a known weakness.

  `assume` does not handle predicates with complex numbers. If a predicate contains a complex number `assume` returns `inconsistent` or `redunant`.

  `assume` evaluates its arguments.

  See also `is`, `facts`, `forget`, `context`, and `declare`.

  Examples:

      (%i1) assume (xx > 0, yy < -1, zz >= 0);
      (%o1)              [xx > 0, yy < - 1, zz >= 0]
      (%i2) assume (aa < bb and bb < cc);
      (%o2)                  [bb > aa, cc > bb]
      (%i3) facts ();
      (%o3)     [xx > 0, - 1 > yy, zz >= 0, bb > aa, cc > bb]
      (%i4) is (xx > yy);
      (%o4)                         true
      (%i5) is (yy < -yy);
      (%o5)                         true
      (%i6) is (sinh (bb - aa) > 0);
      (%o6)                         true
      (%i7) forget (bb > aa);
      (%o7)                       [bb > aa]
      (%i8) prederror : false;
      (%o8)                         false
      (%i9) is (sinh (bb - aa) > 0);
      (%o9)                        unknown
      (%i10) is (bb^2 < cc^2);
      (%o10)                       unknown

  ·

  @ref{Category: Declarations and inferences}

Option variable: assumescalar

  Default value: `true`

  `assumescalar` helps govern whether expressions `expr` for which `nonscalarp (expr)` is `false` are assumed to behave like scalars for certain transformations.

  Let `expr` represent any expression other than a list or a matrix, and let `[1, 2, 3]` represent any list or matrix. Then `expr . [1, 2, 3]` yields `[expr, 2 expr, 3 expr]` if `assumescalar` is `true`, or `scalarp (expr)` is `true`, or `constantp (expr)` is `true`.

  If `assumescalar` is `true`, such expressions will behave like scalars only for commutative operators, but not for noncommutative multiplication `.`.

  When `assumescalar` is `false`, such expressions will behave like non-scalars.

  When `assumescalar` is `all`, such expressions will behave like scalars for all the operators listed above.

  ·

  @ref{Category: Declarations and inferences}

Option variable: assume_pos

  Default value: `false`

  When `assume_pos` is `true` and the sign of a parameter x cannot be determined from the current context or other considerations, `sign` and `asksign (x)` return `true`. This may forestall some automatically-generated `asksign` queries, such as may arise from `integrate` or other computations.

  By default, a parameter is x such that `symbolp (x)` or `subvarp (x)`. The class of expressions considered parameters can be modified to some extent via the variable `assume_pos_pred`.

  `sign` and `asksign` attempt to deduce the sign of expressions from the sign of operands within the expression. For example, if `a` and `b` are both positive, then `a + b` is also positive.

  However, there is no way to bypass all `asksign` queries. In particular, when the `asksign` argument is a difference `x - y` or a logarithm `log(x)`, `asksign` always requests an input from the user, even when `assume_pos` is `true` and `assume_pos_pred` is a function which returns `true` for all arguments.

  ·

  @ref{Category: Declarations and inferences}

Option variable: assume_pos_pred

  Default value: `false`

  When `assume_pos_pred` is assigned the name of a function or a lambda expression of one argument x, that function is called to determine whether x is considered a parameter for the purpose of `assume_pos`. `assume_pos_pred` is ignored when `assume_pos` is `false`.

  The `assume_pos_pred` function is called by `sign` and `asksign` with an argument x which is either an atom, a subscripted variable, or a function call expression. If the `assume_pos_pred` function returns `true`, x is considered a parameter for the purpose of `assume_pos`.

  By default, a parameter is x such that `symbolp (x)` or `subvarp (x)`.

  See also `assume` and `assume_pos`.

  Examples:

      (%i1) assume_pos: true$
      (%i2) assume_pos_pred: symbolp$
      (%i3) sign (a);
      (%o3)                          pos
      (%i4) sign (a[1]);
      (%o4)                          pnz
      (%i5) assume_pos_pred: lambda ([x], display (x), true)$
      (%i6) asksign (a);
                                    x = a

      (%o6)                          pos
      (%i7) asksign (a[1]);
                                   x = a
                                        1

      (%o7)                          pos
      (%i8) asksign (foo (a));
                                 x = foo(a)

      (%o8)                          pos
      (%i9) asksign (foo (a) + bar (b));
                                 x = foo(a)

                                 x = bar(b)

      (%o9)                          pos
      (%i10) asksign (log (a));
                                    x = a

      Is  a - 1  positive, negative, or zero?

      p;
      (%o10)                         pos
      (%i11) asksign (a - b);
                                    x = a

                                    x = b

                                    x = a

                                    x = b

      Is  b - a  positive, negative, or zero?

      p;
      (%o11)                         neg

  ·

  @ref{Category: Declarations and inferences}

Option variable: context

  Default value: `initial`

  `context` names the collection of facts maintained by `assume` and `forget`. `assume` adds facts to the collection named by `context`, while `forget` removes facts.

  Binding `context` to a name foo changes the current context to foo. If the specified context foo does not yet exist, it is created automatically by a call to `newcontext`. The specified context is activated automatically.

  See `contexts` for a general description of the context mechanism.

  ·

  @ref{Category: Declarations and inferences}

Option variable: contexts

  Default value: `[initial, global]`

  `contexts` is a list of the contexts which currently exist, including the currently active context.

  The context mechanism makes it possible for a user to bind together and name a collection of facts, called a context. Once this is done, the user can have Maxima assume or forget large numbers of facts merely by activating or deactivating their context.

  Any symbolic atom can be a context, and the facts contained in that context will be retained in storage until destroyed one by one by calling `forget` or destroyed as a whole by calling `kill` to destroy the context to which they belong.

  Contexts exist in a hierarchy, with the root always being the context `global`, which contains information about Maxima that some functions need. When in a given context, all the facts in that context are "active" (meaning that they are used in deductions and retrievals) as are all the facts in any context which is a subcontext of the active context.

  When a fresh Maxima is started up, the user is in a context called `initial`, which has `global` as a subcontext.

  See also `facts`, `newcontext`, `supcontext`, `killcontext`, `activate`, `deactivate`, `assume`, and `forget`.

  ·

  @ref{Category: Declarations and inferences}

Function: deactivate (context_1, …, context_n)

  Deactivates the specified contexts context_1, …, context_n.

  ·

  @ref{Category: Declarations and inferences}

Function: facts
`facts` (item)
`facts` ()

  If item is the name of a context, `facts (item)` returns a list of the facts in the specified context.

  If item is not the name of a context, `facts (item)` returns a list of the facts known about item in the current context. Facts that are active, but in a different context, are not listed.

  `facts ()` (i.e., without an argument) lists the current context.

  ·

  @ref{Category: Declarations and inferences}

Function: forget
`forget` (pred_1, …, pred_n)
`forget` (L)

  Removes predicates established by `assume`. The predicates may be expressions equivalent to (but not necessarily identical to) those previously assumed.

  `forget (L)`, where L is a list of predicates, forgets each item on the list.

  ·

  @ref{Category: Declarations and inferences}

Function: is (expr)

  Attempts to determine whether the predicate expr is provable from the facts in the `assume` database.

  If the predicate is provably `true` or `false`, `is` returns `true` or `false`, respectively. Otherwise, the return value is governed by the global flag `prederror`. When `prederror` is `true`, `is` complains with an error message. Otherwise, `is` returns `unknown`.

  `ev(expr, pred)` (which can be written `expr, pred` at the interactive prompt) is equivalent to `is(expr)`.

  See also `assume`, `facts`, and `maybe`.

  Examples:

  `is` causes evaluation of predicates.

      (%i1) %pi > %e;
      (%o1)                       %pi > %e
      (%i2) is (%pi > %e);
      (%o2)                         true

  `is` attempts to derive predicates from the `assume` database.

      (%i1) assume (a > b);
      (%o1)                        [a > b]
      (%i2) assume (b > c);
      (%o2)                        [b > c]
      (%i3) is (a < b);
      (%o3)                         false
      (%i4) is (a > c);
      (%o4)                         true
      (%i5) is (equal (a, c));
      (%o5)                         false

  If `is` can neither prove nor disprove a predicate from the `assume` database, the global flag `prederror` governs the behavior of `is`.

      (%i1) assume (a > b);
      (%o1)                        [a > b]
      (%i2) prederror: true$
      (%i3) is (a > 0);
      Maxima was unable to evaluate the predicate:
      a > 0
       -- an error.  Quitting.  To debug this try debugmode(true);
      (%i4) prederror: false$
      (%i5) is (a > 0);
      (%o5)                        unknown

  ·

  @ref{Category: Predicate functions} · @ref{Category: Declarations and inferences}

Function: killcontext (context_1, …, context_n)

  Kills the contexts context_1, …, context_n.

  If one of the contexts is the current context, the new current context will become the first available subcontext of the current context which has not been killed. If the first available unkilled context is `global` then `initial` is used instead. If the `initial` context is killed, a new, empty `initial` context is created.

  `killcontext` refuses to kill a context which is currently active, either because it is a subcontext of the current context, or by use of the function `activate`.

  `killcontext` evaluates its arguments. `killcontext` returns `done`.

  ·

  @ref{Category: Declarations and inferences}

Function: maybe (expr)

  Attempts to determine whether the predicate expr is provable from the facts in the `assume` database.

  If the predicate is provably `true` or `false`, `maybe` returns `true` or `false`, respectively. Otherwise, `maybe` returns `unknown`.

  `maybe` is functionally equivalent to `is` with `prederror: false`, but the result is computed without actually assigning a value to `prederror`.

  See also `assume`, `facts`, and `is`.

  Examples:

      (%i1) maybe (x > 0);
      (%o1)                        unknown
      (%i2) assume (x > 1);
      (%o2)                        [x > 1]
      (%i3) maybe (x > 0);
      (%o3)                         true

  ·

  @ref{Category: Predicate functions} · @ref{Category: Declarations and inferences}

Function: newcontext
`newcontext` (name)
`newcontext` ()

  Creates a new, empty context, called name, which has `global` as its only subcontext. The newly-created context becomes the currently active context.

  If name is not specified, a new name is created (via `gensym`) and returned.

  `newcontext` evaluates its argument. `newcontext` returns name (if specified) or the new context name.

  ·

  @ref{Category: Declarations and inferences}

Function: sign (expr)

  Attempts to determine the sign of expr on the basis of the facts in the current data base. It returns one of the following answers: `pos` (positive), `neg` (negative), `zero`, `pz` (positive or zero), `nz` (negative or zero), `pn` (positive or negative), or `pnz` (positive, negative, or zero, i.e. nothing known).

  ·

  @ref{Category: Declarations and inferences}

Function: supcontext
`supcontext` (name, context)
`supcontext` (name)
`supcontext` ()

  Creates a new context, called name, which has context as a subcontext. context must exist.

  If context is not specified, the current context is assumed.

  If name is not specified, a new name is created (via `gensym`) and returned.

  `supcontext` evaluates its argument. `supcontext` returns name (if specified) or the new context name.

  ·

  @ref{Category: Declarations and inferences}

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## 11.4 Functions and Variables for Predicates

Function: charfun (p)

  Return 0 when the predicate p evaluates to `false`; return 1 when the predicate evaluates to `true`. When the predicate evaluates to something other than `true` or `false` (unknown), return a noun form.

  Examples:

      (%i1) charfun (x < 1);
      (%o1)                    charfun(x < 1)
      (%i2) subst (x = -1, %);
      (%o2)                           1
      (%i3) e : charfun ('"and" (-1 < x, x < 1))$
      (%i4) [subst (x = -1, e), subst (x = 0, e), subst (x = 1, e)];
      (%o4)                       [0, 1, 0]

  ·

  @ref{Category: Mathematical functions}

Function: compare (x, y)

  Return a comparison operator op (`<`, `<=`, `>`, `>=`, `=`, or `#`) such that `is (x op y)` evaluates to `true`; when either x or y depends on `%i` and `x # y`, return `notcomparable`; when there is no such operator or Maxima isn't able to determine the operator, return `unknown`.

  Examples:

      (%i1) compare (1, 2);
      (%o1)                           <
      (%i2) compare (1, x);
      (%o2)                        unknown
      (%i3) compare (%i, %i);
      (%o3)                           =
      (%i4) compare (%i, %i + 1);
      (%o4)                     notcomparable
      (%i5) compare (1/x, 0);
      (%o5)                           #
      (%i6) compare (x, abs(x));
      (%o6)                          <=

  The function `compare` doesn't try to determine whether the real domains of its arguments are nonempty; thus

      (%i1) compare (acos (x^2 + 1), acos (x^2 + 1) + 1);
      (%o1)                           <

  The real domain of `acos (x^2 + 1)` is empty.

  ·

  @ref{Category: Declarations and inferences}

Function: equal (a, b)

  Represents equivalence, that is, equal value.

  By itself, `equal` does not evaluate or simplify. The function `is` attempts to evaluate `equal` to a Boolean value. `is(equal(a, b))` returns `true` (or `false`) if and only if a and b are equal (or not equal) for all possible values of their variables, as determined by evaluating `ratsimp(a - b)`; if `ratsimp` returns 0, the two expressions are considered equivalent. Two expressions may be equivalent even if they are not syntactically equal (i.e., identical).

  When `is` fails to reduce `equal` to `true` or `false`, the result is governed by the global flag `prederror`. When `prederror` is `true`, `is` complains with an error message. Otherwise, `is` returns `unknown`.

  In addition to `is`, some other operators evaluate `equal` and `notequal` to `true` or `false`, namely `if`, `and`, `or`, and `not`.

  The negation of `equal` is `notequal`.

  Examples:

  By itself, `equal` does not evaluate or simplify.

      (%i1) equal (x^2 - 1, (x + 1) * (x - 1));
                              2
      (%o1)            equal(x  - 1, (x - 1) (x + 1))
      (%i2) equal (x, x + 1);
      (%o2)                    equal(x, x + 1)
      (%i3) equal (x, y);
      (%o3)                      equal(x, y)

  The function `is` attempts to evaluate `equal` to a Boolean value. `is(equal(a, b))` returns `true` when `ratsimp(a - b)` returns 0. Two expressions may be equivalent even if they are not syntactically equal (i.e., identical).

      (%i1) ratsimp (x^2 - 1 - (x + 1) * (x - 1));
      (%o1)                           0
      (%i2) is (equal (x^2 - 1, (x + 1) * (x - 1)));
      (%o2)                         true
      (%i3) is (x^2 - 1 = (x + 1) * (x - 1));
      (%o3)                         false
      (%i4) ratsimp (x - (x + 1));
      (%o4)                          - 1
      (%i5) is (equal (x, x + 1));
      (%o5)                         false
      (%i6) is (x = x + 1);
      (%o6)                         false
      (%i7) ratsimp (x - y);
      (%o7)                         x - y
      (%i8) is (equal (x, y));
      (%o8)                        unknown
      (%i9) is (x = y);
      (%o9)                         false

  When `is` fails to reduce `equal` to `true` or `false`, the result is governed by the global flag `prederror`.

      (%i1) [aa : x^2 + 2*x + 1, bb : x^2 - 2*x - 1];
                          2             2
      (%o1)             [x  + 2 x + 1, x  - 2 x - 1]
      (%i2) ratsimp (aa - bb);
      (%o2)                        4 x + 2
      (%i3) prederror : true;
      (%o3)                         true
      (%i4) is (equal (aa, bb));
      Maxima was unable to evaluate the predicate:
             2             2
      equal(x  + 2 x + 1, x  - 2 x - 1)
       -- an error.  Quitting.  To debug this try debugmode(true);
      (%i5) prederror : false;
      (%o5)                         false
      (%i6) is (equal (aa, bb));
      (%o6)                        unknown

  Some operators evaluate `equal` and `notequal` to `true` or `false`.

      (%i1) if equal (y, y - 1) then FOO else BAR;
      (%o1)                          BAR
      (%i2) eq_1 : equal (x, x + 1);
      (%o2)                    equal(x, x + 1)
      (%i3) eq_2 : equal (y^2 + 2*y + 1, (y + 1)^2);
                               2                   2
      (%o3)             equal(y  + 2 y + 1, (y + 1) )
      (%i4) [eq_1 and eq_2, eq_1 or eq_2, not eq_1];
      (%o4)                  [false, true, true]

  Because `not expr` causes evaluation of expr, `not equal(a, b)` is equivalent to `is(notequal(a, b))`.

      (%i1) [notequal (2*z, 2*z - 1), not equal (2*z, 2*z - 1)];
      (%o1)            [notequal(2 z, 2 z - 1), true]
      (%i2) is (notequal (2*z, 2*z - 1));
      (%o2)                         true

  ·

  @ref{Category: Operators}

Function: notequal (a, b)

  Represents the negation of `equal(a, b)`.

  Examples:

      (%i1) equal (a, b);
      (%o1)                      equal(a, b)
      (%i2) maybe (equal (a, b));
      (%o2)                        unknown
      (%i3) notequal (a, b);
      (%o3)                    notequal(a, b)
      (%i4) not equal (a, b);
      (%o4)                    notequal(a, b)
      (%i5) maybe (notequal (a, b));
      (%o5)                        unknown
      (%i6) assume (a > b);
      (%o6)                        [a > b]
      (%i7) equal (a, b);
      (%o7)                      equal(a, b)
      (%i8) maybe (equal (a, b));
      (%o8)                         false
      (%i9) notequal (a, b);
      (%o9)                    notequal(a, b)
      (%i10) maybe (notequal (a, b));
      (%o10)                        true

  ·

  @ref{Category: Operators}

Function: unknown (expr)

  Returns `true` if and only if expr contains an operator or function not recognized by the Maxima simplifier.

  ·

  @ref{Category: Predicate functions} · @ref{Category: Simplification functions}

Function: zeroequiv (expr, v)

  Tests whether the expression expr in the variable v is equivalent to zero, returning `true`, `false`, or `dontknow`.

  `zeroequiv` has these restrictions:

  1. Do not use functions that Maxima does not know how to differentiate and evaluate.
  2. If the expression has poles on the real line, there may be errors in the result (but this is unlikely to occur).
  3. If the expression contains functions which are not solutions to first order differential equations (e.g. Bessel functions) there may be incorrect results.
  4. The algorithm uses evaluation at randomly chosen points for carefully selected subexpressions. This is always a somewhat hazardous business, although the algorithm tries to minimize the potential for error.

  For example `zeroequiv (sin(2 * x) - 2 * sin(x) * cos(x), x)` returns `true` and `zeroequiv (%e^x + x, x)` returns `false`. On the other hand `zeroequiv (log(a * b) - log(a) - log(b), a)` returns `dontknow` because of the presence of an extra parameter `b`.

  ·

  @ref{Category: Predicate functions}

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