Callable Symbolic Expressions

EXAMPLES:

When you do arithmetic with:

sage: f(x, y, z) = sin(x+y+z)
sage: g(x, y) = y + 2*x
sage: f + g
(x, y, z) |--> 2*x + y + sin(x + y + z)

sage: f(x, y, z) = sin(x+y+z)
sage: g(w, t) = cos(w - t)
sage: f + g
(t, w, x, y, z) |--> cos(-t + w) + sin(x + y + z)

sage: f(x, y, t) = y*(x^2-t)
sage: g(x, y, w) = x + y - cos(w)
sage: f*g
(x, y, t, w) |--> (x^2 - t)*(x + y - cos(w))*y

sage: f(x,y, t) = x+y
sage: g(x, y, w) = w + t
sage: f + g
(x, y, t, w) |--> t + w + x + y

TESTS:

The arguments in the definition must be symbolic variables #10747:

sage: f(1)=2
Traceback (most recent call last):
...
SyntaxError: can't assign to function call

sage: f(x,1)=2
Traceback (most recent call last):
...
SyntaxError: can't assign to function call

sage: f(1,2)=3
Traceback (most recent call last):
...
SyntaxError: can't assign to function call

sage: f(1,2)=x
Traceback (most recent call last):
...
SyntaxError: can't assign to function call

sage: f(x,2)=x
Traceback (most recent call last):
...
SyntaxError: can't assign to function call

class sage.symbolic.callable.CallableSymbolicExpressionFunctor(arguments)

Bases: sage.categories.pushout.ConstructionFunctor

A functor which produces a CallableSymbolicExpressionRing from the SymbolicRing.

EXAMPLES:

sage: from sage.symbolic.callable import CallableSymbolicExpressionFunctor
sage: x,y = var('x,y')
sage: f = CallableSymbolicExpressionFunctor((x,y)); f
CallableSymbolicExpressionFunctor(x, y)
sage: f(SR)
Callable function ring with arguments (x, y)

sage: loads(dumps(f))
CallableSymbolicExpressionFunctor(x, y)

arguments()

EXAMPLES:

sage: from sage.symbolic.callable import CallableSymbolicExpressionFunctor
sage: x,y = var('x,y')
sage: a = CallableSymbolicExpressionFunctor((x,y))
sage: a.arguments()
(x, y)

merge(other)

EXAMPLES:

sage: from sage.symbolic.callable import CallableSymbolicExpressionFunctor
sage: x,y = var('x,y')
sage: a = CallableSymbolicExpressionFunctor((x,))
sage: b = CallableSymbolicExpressionFunctor((y,))
sage: a.merge(b)
CallableSymbolicExpressionFunctor(x, y)

unify_arguments(x)

Takes the variable list from another CallableSymbolicExpression object and compares it with the current CallableSymbolicExpression object’s variable list, combining them according to the following rules:

Let a be self‘s variable list, let b be y‘s variable list.

1. If a == b, then the variable lists are identical, so return that variable list.
2. If a \(\neq\) b, then check if the first \(n\) items in a are the first \(n\) items in b, or vice versa. If so, return a list with these \(n\) items, followed by the remaining items in a and b sorted together in alphabetical order.

Note

When used for arithmetic between CallableSymbolicExpression‘s, these rules ensure that the set of CallableSymbolicExpression‘s will have certain properties. In particular, it ensures that the set is a commutative ring, i.e., the order of the input variables is the same no matter in which order arithmetic is done.

INPUT:

• x - A CallableSymbolicExpression

OUTPUT: A tuple of variables.

EXAMPLES:

sage: from sage.symbolic.callable import CallableSymbolicExpressionFunctor
sage: x,y = var('x,y')
sage: a = CallableSymbolicExpressionFunctor((x,))
sage: b = CallableSymbolicExpressionFunctor((y,))
sage: a.unify_arguments(b)
(x, y)

AUTHORS:

• Bobby Moretti: thanks to William Stein for the rules

class sage.symbolic.callable.CallableSymbolicExpressionRingFactory

Bases: sage.structure.factory.UniqueFactory

create_key(args, check=True)

EXAMPLES:

sage: x,y = var('x,y')
sage: CallableSymbolicExpressionRing.create_key((x,y))
(x, y)

create_object(version, key, **extra_args)

Returns a CallableSymbolicExpressionRing given a version and a key.

EXAMPLES:

sage: x,y = var('x,y')
sage: CallableSymbolicExpressionRing.create_object(0, (x, y))
Callable function ring with arguments (x, y)

class sage.symbolic.callable.CallableSymbolicExpressionRing_class(arguments)

Bases: sage.symbolic.ring.SymbolicRing

EXAMPLES:

We verify that coercion works in the case where x is not an instance of SymbolicExpression, but its parent is still the SymbolicRing:

sage: f(x) = 1
sage: f*e
x |--> e

args()

Returns the arguments of self. The order that the variables appear in self.arguments() is the order that is used in evaluating the elements of self.

EXAMPLES:

sage: x,y = var('x,y')
sage: f(x,y) = 2*x+y
sage: f.parent().arguments()
(x, y)
sage: f(y,x) = 2*x+y
sage: f.parent().arguments()
(y, x)

arguments()

Returns the arguments of self. The order that the variables appear in self.arguments() is the order that is used in evaluating the elements of self.

EXAMPLES:

sage: x,y = var('x,y')
sage: f(x,y) = 2*x+y
sage: f.parent().arguments()
(x, y)
sage: f(y,x) = 2*x+y
sage: f.parent().arguments()
(y, x)

construction()

EXAMPLES:

sage: f(x,y) = x^2 + y
sage: f.parent().construction()
(CallableSymbolicExpressionFunctor(x, y), Symbolic Ring)

sage.symbolic.callable.is_CallableSymbolicExpression(x)

Returns True if x is a callable symbolic expression.

EXAMPLES:

sage: from sage.symbolic.callable import is_CallableSymbolicExpression
sage: var('a x y z')
(a, x, y, z)
sage: f(x,y) = a + 2*x + 3*y + z
sage: is_CallableSymbolicExpression(f)
True
sage: is_CallableSymbolicExpression(a+2*x)
False
sage: def foo(n): return n^2
...
sage: is_CallableSymbolicExpression(foo)
False

sage.symbolic.callable.is_CallableSymbolicExpressionRing(x)

Return True if x is a callable symbolic expression ring.

INPUT:

• x - object

OUTPUT: bool

EXAMPLES:

sage: from sage.symbolic.callable import is_CallableSymbolicExpressionRing
sage: is_CallableSymbolicExpressionRing(QQ)
False
sage: var('x,y,z')
(x, y, z)
sage: is_CallableSymbolicExpressionRing(CallableSymbolicExpressionRing((x,y,z)))
True