def restriction(cls, self, parameters, variable, restricted_domain):
"""
Restrict the domain
INPUT:
- ``restricted_domain`` -- a
:class:`~sage.sets.real_set.RealSet` or something that
defines one.
OUTPUT:
A new piecewise function obtained by restricting the domain.
EXAMPLES::
sage: f = piecewise([((-oo, oo), x)]); f
piecewise(x|-->x on (-oo, +oo); x)
sage: f.restriction([[-1,1], [3,3]])
piecewise(x|-->x on [-1, 1] + {3}; x)
"""
restricted_domain = RealSet(*restricted_domain)
new_param = []
for domain, func in parameters:
domain = domain.intersection(restricted_domain)
new_param.append((domain, func))
return piecewise(new_param, var=variable)
def domain(cls, self, parameters, variable):
"""
Return the domain
OUTPUT:
The union of the domains of the individual pieces as a
:class:`~sage.sets.real_set.RealSet`.
EXAMPLES::
sage: f = piecewise([([0,0], sin(x)), ((0,2), cos(x))]); f
piecewise(x|-->sin(x) on {0}, x|-->cos(x) on (0, 2); x)
sage: f.domain()
[0, 2)
"""
intervals = []
for domain, func in parameters:
intervals += list(domain)
return RealSet(*intervals)
def __call__(self, function_pieces, **kwds):
r"""
Piecewise functions
INPUT:
- ``function_pieces`` -- a list of pairs consisting of a
domain and a symbolic function.
- ``var=x`` -- a symbolic variable or ``None`` (default). The
real variable in which the function is piecewise in.
OUTPUT:
A piecewise-defined function. A ``ValueError`` will be raised
if the domains of the pieces are not pairwise disjoint.
EXAMPLES::
sage: my_abs = piecewise([((-1, 0), -x), ([0, 1], x)], var=x); my_abs
piecewise(x|-->-x on (-1, 0), x|-->x on [0, 1]; x)
sage: [ my_abs(i/5) for i in range(-4, 5)]
[4/5, 3/5, 2/5, 1/5, 0, 1/5, 2/5, 3/5, 4/5]
TESTS::
sage: piecewise([([-1, 0], -x), ([0, 1], x)], var=x)
Traceback (most recent call last):
...
ValueError: domains must be pairwise disjoint
sage: step = piecewise([((-1, 0), -1), ([0, 0], 0), ((0, 1), 1)], var=x); step
piecewise(x|-->-1 on (-1, 0), x|-->0 on {0}, x|-->1 on (0, 1); x)
sage: step(-1/2), step(0), step(1/2)
(-1, 0, 1)
"""
from types import FunctionType
var = kwds.pop('var', None)
parameters = []
domain_list = []
for piece in function_pieces:
domain, function = piece
if not isinstance(domain, RealSet):
domain = RealSet(domain)
if domain.is_empty():
continue
if isinstance(function, FunctionType):
if var is None:
var = SR.var('x')
if function.func_code.co_argcount == 0:
function = function()
else:
function = function(var)
function = SR(function)
if var is None and len(function.variables()) > 0:
var = function.variables()[0]
parameters.append((domain, function))
domain_list.append(domain)
if not RealSet.are_pairwise_disjoint(*domain_list):
raise ValueError('domains must be pairwise disjoint')
if var is None:
var = self.default_variable()
parameters = SR._force_pyobject(tuple(parameters), recursive=False)
return BuiltinFunction.__call__(self, parameters, var, **kwds)
def piecewise_add(cls, self, parameters, variable, other):
"""
Return a new piecewise function with domain the union
of the original domains and functions summed. Undefined
intervals in the union domain get function value `0`.
EXAMPLES::
sage: f = piecewise([([0,1], 1), ((2,3), x)])
sage: g = piecewise([((1/2, 2), x)])
sage: f.piecewise_add(g).unextend_zero()
piecewise(x|-->1 on (0, 1/2], x|-->x + 1 on (1/2, 1], x|-->x on (1, 2) + (2, 3); x)
"""
points = ([minus_infinity] +
sorted(set(self.end_points() + other.end_points())) +
[infinity])
domain = []
funcs = []
contains_lower = False
contains_upper = False
for i in range(len(points)-1):
try:
contains_lower = (self.domain().contains(points[i]) or
other.domain().contains(points[i])) and not contains_upper
contains_upper = (self.domain().contains(points[i+1]) or
other.domain().contains(points[i+1]))
if contains_lower:
if contains_upper:
rs = RealSet.closed(points[i],points[i+1])
else:
rs = RealSet.closed_open(points[i],points[i+1])
else:
if contains_upper:
rs = RealSet.open_closed(points[i],points[i+1])
else:
rs = RealSet.open(points[i],points[i+1])
point = (points[i+1] + points[i])/2
except ValueError:
if points[i] == minus_infinity and points[i+1] == infinity:
rs = RealSet.open(minus_infinity, infinity)
point = 0
elif points[i] == minus_infinity:
if contains_lower:
rs = RealSet.unbounded_below_closed(points[i+1])
else:
rs = RealSet.unbounded_below_open(points[i+1])
point = points[i+1]-1
elif points[i+1] == infinity:
if contains_upper:
rs = RealSet.unbounded_above_closed(points[i])
else:
rs = RealSet.unbounded_above_open(points[i])
point = points[i]+1
else:
raise
try:
ex1 = self.expression_at(point)
except ValueError:
ex1 = 0
try:
ex2 = other.expression_at(point)
except ValueError:
ex2 = 0
ex = ex1 + ex2
if i>0 and funcs[-1] == ex:
# extend the previous domain
rs += domain[-1]
domain[-1] = rs
else:
domain += rs
funcs.append(ex)
return piecewise(zip(domain, funcs))
from sage.sets.real_set import RealSet
from sage.structure.element import Matrix as MatrixClass
from sage.structure.factorization_integer import IntegerFactorization
from sage.symbolic.expression import Expression
from sage.symbolic.relation import solve
from sage.symbolic.ring import SR
pair_keep = staticmethod(lambda i, j: (i, j))
pair_swap = staticmethod(lambda i, j: (j, i))
CHECK_LEVELS = 4
INTERVAL = {
(True, True): RealSet.closed,
(True, False): RealSet.closed_open,
(True, None): lambda l, u: RealSet.unbounded_above_closed(l),
(False, True): RealSet.open_closed,
(False, False): RealSet.open,
(False, None): lambda l, u: RealSet.unbounded_above_open(l),
(None, True): lambda l, u: RealSet.unbounded_below_closed(u),
(None, False): lambda l, u: RealSet.unbounded_below_open(u),
(None, None): lambda l, u: RealSet().complement()
}
def checklist(checks, inherit=None):
"""
Initialize the list of feasibility checking functions
and return a decorator for the functions.
"""
if inherit is None:
def piecewise_add(cls, self, parameters, variable, other):
"""
Return a new piecewise function with domain the union
of the original domains and functions summed. Undefined
intervals in the union domain get function value `0`.
EXAMPLES::
sage: f = piecewise([([0,1], 1), ((2,3), x)])
sage: g = piecewise([((1/2, 2), x)])
sage: f.piecewise_add(g).unextend_zero()
piecewise(x|-->1 on (0, 1/2], x|-->x + 1 on (1/2, 1], x|-->x on (1, 2) + (2, 3); x)
"""
points = ([minus_infinity] +
sorted(set(self.end_points() + other.end_points())) +
[infinity])
domain = []
funcs = []
contains_lower = False
contains_upper = False
for i in range(len(points) - 1):
try:
contains_lower = (self.domain().contains(points[i])
or other.domain().contains(
points[i])) and not contains_upper
contains_upper = (self.domain().contains(points[i + 1]) or
other.domain().contains(points[i + 1]))
if contains_lower:
if contains_upper:
rs = RealSet.closed(points[i], points[i + 1])
else:
rs = RealSet.closed_open(points[i], points[i + 1])
else:
if contains_upper:
rs = RealSet.open_closed(points[i], points[i + 1])
else:
rs = RealSet.open(points[i], points[i + 1])
point = (points[i + 1] + points[i]) / 2
except ValueError:
if points[i] == minus_infinity and points[i +
1] == infinity:
rs = RealSet.open(minus_infinity, infinity)
point = 0
elif points[i] == minus_infinity:
if contains_lower:
rs = RealSet.unbounded_below_closed(points[i + 1])
else:
rs = RealSet.unbounded_below_open(points[i + 1])
point = points[i + 1] - 1
elif points[i + 1] == infinity:
if contains_upper:
rs = RealSet.unbounded_above_closed(points[i])
else:
rs = RealSet.unbounded_above_open(points[i])
point = points[i] + 1
else:
raise
try:
ex1 = self.expression_at(point)
except ValueError:
ex1 = 0
try:
ex2 = other.expression_at(point)
except ValueError:
ex2 = 0
ex = ex1 + ex2
if i > 0 and funcs[-1] == ex:
# extend the previous domain
rs += domain[-1]
domain[-1] = rs
else:
domain += rs
funcs.append(ex)
return piecewise(zip(domain, funcs))
def __call__(self, function_pieces, **kwds):
r"""
Piecewise functions
INPUT:
- ``function_pieces`` -- a list of pairs consisting of a
domain and a symbolic function.
- ``var=x`` -- a symbolic variable or ``None`` (default). The
real variable in which the function is piecewise in.
OUTPUT:
A piecewise-defined function. A ``ValueError`` will be raised
if the domains of the pieces are not pairwise disjoint.
EXAMPLES::
sage: my_abs = piecewise([((-1, 0), -x), ([0, 1], x)], var=x); my_abs
piecewise(x|-->-x on (-1, 0), x|-->x on [0, 1]; x)
sage: [ my_abs(i/5) for i in range(-4, 5)]
[4/5, 3/5, 2/5, 1/5, 0, 1/5, 2/5, 3/5, 4/5]
TESTS::
sage: piecewise([([-1, 0], -x), ([0, 1], x)], var=x)
Traceback (most recent call last):
...
ValueError: domains must be pairwise disjoint
sage: step = piecewise([((-1, 0), -1), ([0, 0], 0), ((0, 1), 1)], var=x); step
piecewise(x|-->-1 on (-1, 0), x|-->0 on {0}, x|-->1 on (0, 1); x)
sage: step(-1/2), step(0), step(1/2)
(-1, 0, 1)
"""
from types import FunctionType
var = kwds.pop('var', None)
parameters = []
domain_list = []
for piece in function_pieces:
domain, function = piece
if not isinstance(domain, RealSet):
domain = RealSet(domain)
if domain.is_empty():
continue
if isinstance(function, FunctionType):
if var is None:
var = SR.var('x')
if function.func_code.co_argcount == 0:
function = function()
else:
function = function(var)
function = SR(function)
if var is None and len(function.variables()) > 0:
var = function.variables()[0]
parameters.append((domain, function))
domain_list.append(domain)
if not RealSet.are_pairwise_disjoint(*domain_list):
raise ValueError('domains must be pairwise disjoint')
if var is None:
var = self.default_variable()
parameters = SR._force_pyobject(tuple(parameters), recursive=False)
return BuiltinFunction.__call__(self, parameters, var, **kwds)
