def test_is_monotonic():
"""Test whether is_monotonic returns correct value."""
assert is_monotonic(1 / (x**2 - 3 * x), Interval.open(Rational(3, 2), 3))
assert is_monotonic(1 / (x**2 - 3 * x), Interval.open(1.5, 3))
assert is_monotonic(1 / (x**2 - 3 * x), Interval.Lopen(3, oo))
assert is_monotonic(x**3 - 3 * x**2 + 4 * x, S.Reals)
assert not is_monotonic(-x**2, S.Reals)
assert is_monotonic(x**2 + y + 1, Interval(1, 2), x)
raises(NotImplementedError, lambda: is_monotonic(x**2 + y + 1))
def test_is_strictly_decreasing():
"""Test whether is_strictly_decreasing returns correct value."""
assert is_strictly_decreasing(1 / (x**2 - 3 * x), Interval.Lopen(3, oo))
assert not is_strictly_decreasing(1 / (x**2 - 3 * x),
Interval.Ropen(-oo, Rational(3, 2)))
assert not is_strictly_decreasing(-x**2, Interval(-oo, 0))
assert not is_strictly_decreasing(1)
assert is_strictly_decreasing(1 / (x**2 - 3 * x),
Interval.open(Rational(3, 2), 3))
assert is_strictly_decreasing(1 / (x**2 - 3 * x), Interval.open(1.5, 3))
def test_is_decreasing():
"""Test whether is_decreasing returns correct value."""
b = Symbol('b', positive=True)
assert is_decreasing(1 / (x**2 - 3 * x), Interval.open(Rational(3, 2), 3))
assert is_decreasing(1 / (x**2 - 3 * x), Interval.open(1.5, 3))
assert is_decreasing(1 / (x**2 - 3 * x), Interval.Lopen(3, oo))
assert not is_decreasing(1 / (x**2 - 3 * x),
Interval.Ropen(-oo, Rational(3, 2)))
assert not is_decreasing(-x**2, Interval(-oo, 0))
assert not is_decreasing(-x**2 * b, Interval(-oo, 0), x)
def test_is_strictly_increasing():
"""Test whether is_strictly_increasing returns correct value."""
assert is_strictly_increasing(
4*x**3 - 6*x**2 - 72*x + 30, Interval.Ropen(-oo, -2))
assert is_strictly_increasing(
4*x**3 - 6*x**2 - 72*x + 30, Interval.Lopen(3, oo))
assert not is_strictly_increasing(
4*x**3 - 6*x**2 - 72*x + 30, Interval.open(-2, 3))
assert not is_strictly_increasing(-x**2, Interval(0, oo))
assert not is_strictly_decreasing(1)
assert is_strictly_increasing(4*x**3 - 6*x**2 - 72*x + 30, Interval.open(-2, 3)) is False
def test_is_monotonic():
"""Test whether is_monotonic returns correct value."""
assert is_monotonic(1/(x**2 - 3*x), Interval.open(1.5, 3))
assert is_monotonic(1/(x**2 - 3*x), Interval.Lopen(3, oo))
assert is_monotonic(x**3 - 3*x**2 + 4*x, S.Reals)
assert not is_monotonic(-x**2, S.Reals)
assert is_monotonic(x**2 + y + 1, Interval(1, 2), x)
def test_is_monotonic():
"""Test whether is_monotonic returns correct value."""
assert is_monotonic(1 / (x**2 - 3 * x), Interval.open(1.5, 3))
assert is_monotonic(1 / (x**2 - 3 * x), Interval.Lopen(3, oo))
assert is_monotonic(x**3 - 3 * x**2 + 4 * x, S.Reals)
assert not is_monotonic(-x**2, S.Reals)
assert is_monotonic(x**2 + y + 1, Interval(1, 2), x)
def test_is_decreasing():
assert is_decreasing(1 / (x**2 - 3 * x), Interval.open(1.5, 3))
assert is_decreasing(1 / (x**2 - 3 * x), Interval.Lopen(3, oo))
assert is_decreasing(1 / (x**2 - 3 * x), Interval.Ropen(-oo,
S(3) / 2)) is False
assert is_decreasing(-x**2, Interval(-oo, 0)) is False
assert is_decreasing(-x**2 * b, Interval(-oo, 0), x) is False
def test_SetExpr_Interval_div():
# TODO: some expressions cannot be calculated due to bugs (currently
# commented):
assert SetExpr(Interval(-3, -2)) / SetExpr(Interval(-2, 1)) == SetExpr(
Interval(-oo, oo))
assert SetExpr(Interval(2, 3)) / SetExpr(Interval(-2, 2)) == SetExpr(
Interval(-oo, oo))
assert SetExpr(Interval(-3, -2)) / SetExpr(Interval(0, 4)) == SetExpr(
Interval(-oo, Rational(-1, 2)))
assert SetExpr(Interval(2, 4)) / SetExpr(Interval(-3, 0)) == SetExpr(
Interval(-oo, Rational(-2, 3)))
assert SetExpr(Interval(2, 4)) / SetExpr(Interval(0, 3)) == SetExpr(
Interval(Rational(2, 3), oo))
# assert SetExpr(Interval(0, 1))/SetExpr(Interval(0, 1)) == SetExpr(Interval(0, oo))
# assert SetExpr(Interval(-1, 0))/SetExpr(Interval(0, 1)) == SetExpr(Interval(-oo, 0))
assert SetExpr(Interval(-1, 2)) / SetExpr(Interval(-2, 2)) == SetExpr(
Interval(-oo, oo))
assert 1 / SetExpr(Interval(-1, 2)) == SetExpr(
Union(Interval(-oo, -1), Interval(S.Half, oo)))
assert 1 / SetExpr(Interval(0, 2)) == SetExpr(Interval(S.Half, oo))
assert (-1) / SetExpr(Interval(0, 2)) == SetExpr(
Interval(-oo, Rational(-1, 2)))
assert 1 / SetExpr(Interval(-oo, 0)) == SetExpr(Interval.open(-oo, 0))
assert 1 / SetExpr(Interval(-1, 0)) == SetExpr(Interval(-oo, -1))
def test_is_strictly_increasing():
assert is_strictly_increasing(4 * x**3 - 6 * x**2 - 72 * x + 30,
Interval.Ropen(-oo, -2))
assert is_strictly_increasing(4 * x**3 - 6 * x**2 - 72 * x + 30,
Interval.Lopen(3, oo))
assert is_strictly_increasing(4 * x**3 - 6 * x**2 - 72 * x + 30,
Interval.open(-2, 3)) is False
assert is_strictly_increasing(-x**2, Interval(0, oo)) is False
def test_is_strictly_decreasing():
"""Test whether is_strictly_decreasing returns correct value."""
assert is_strictly_decreasing(1/(x**2 - 3*x), Interval.Lopen(3, oo))
assert not is_strictly_decreasing(
1/(x**2 - 3*x), Interval.Ropen(-oo, S(3)/2))
assert not is_strictly_decreasing(-x**2, Interval(-oo, 0))
assert not is_strictly_decreasing(1)
assert is_strictly_decreasing(1/(x**2 - 3*x), Interval.open(1.5, 3))
def test_is_decreasing():
"""Test whether is_decreasing returns correct value."""
b = Symbol('b', positive=True)
assert is_decreasing(1/(x**2 - 3*x), Interval.open(1.5, 3))
assert is_decreasing(1/(x**2 - 3*x), Interval.Lopen(3, oo))
assert not is_decreasing(1/(x**2 - 3*x), Interval.Ropen(-oo, S(3)/2))
assert not is_decreasing(-x**2, Interval(-oo, 0))
assert not is_decreasing(-x**2*b, Interval(-oo, 0), x)
def test_SetExpr_Interval_pow():
assert SetExpr(Interval(0, 2))**2 == SetExpr(Interval(0, 4))
assert SetExpr(Interval(-1, 1))**2 == SetExpr(Interval(0, 1))
assert SetExpr(Interval(1, 2))**2 == SetExpr(Interval(1, 4))
assert SetExpr(Interval(-1, 2))**3 == SetExpr(Interval(-1, 8))
assert SetExpr(Interval(-1, 1))**0 == SetExpr(FiniteSet(1))
#assert SetExpr(Interval(1, 2))**Rational(5, 2) == SetExpr(Interval(1, 4*sqrt(2)))
#assert SetExpr(Interval(-1, 2))**Rational(1, 3) == SetExpr(Interval(-1, 2**Rational(1, 3)))
#assert SetExpr(Interval(0, 2))**S.Half == SetExpr(Interval(0, sqrt(2)))
#assert SetExpr(Interval(-4, 2))**Rational(2, 3) == SetExpr(Interval(0, 2*2**Rational(1, 3)))
#assert SetExpr(Interval(-1, 5))**S.Half == SetExpr(Interval(0, sqrt(5)))
#assert SetExpr(Interval(-oo, 2))**S.Half == SetExpr(Interval(0, sqrt(2)))
#assert SetExpr(Interval(-2, 3))**(Rational(-1, 4)) == SetExpr(Interval(0, oo))
assert SetExpr(Interval(1, 5))**(-2) == SetExpr(Interval(Rational(1, 25), 1))
assert SetExpr(Interval(-1, 3))**(-2) == SetExpr(Interval(0, oo))
assert SetExpr(Interval(0, 2))**(-2) == SetExpr(Interval(Rational(1, 4), oo))
assert SetExpr(Interval(-1, 2))**(-3) == SetExpr(Union(Interval(-oo, -1), Interval(Rational(1, 8), oo)))
assert SetExpr(Interval(-3, -2))**(-3) == SetExpr(Interval(Rational(-1, 8), Rational(-1, 27)))
assert SetExpr(Interval(-3, -2))**(-2) == SetExpr(Interval(Rational(1, 9), Rational(1, 4)))
#assert SetExpr(Interval(0, oo))**S.Half == SetExpr(Interval(0, oo))
#assert SetExpr(Interval(-oo, -1))**Rational(1, 3) == SetExpr(Interval(-oo, -1))
#assert SetExpr(Interval(-2, 3))**(Rational(-1, 3)) == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-oo, 0))**(-2) == SetExpr(Interval.open(0, oo))
assert SetExpr(Interval(-2, 0))**(-2) == SetExpr(Interval(Rational(1, 4), oo))
assert SetExpr(Interval(Rational(1, 3), S.Half))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(0, S.Half))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(S.Half, 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(0, 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(2, 3))**oo == SetExpr(FiniteSet(oo))
assert SetExpr(Interval(1, 2))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(S.Half, 3))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(Rational(-1, 3), Rational(-1, 4)))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(-1, Rational(-1, 2)))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-3, -2))**oo == SetExpr(FiniteSet(-oo, oo))
assert SetExpr(Interval(-2, -1))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-2, Rational(-1, 2)))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(Rational(-1, 2), S.Half))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(Rational(-1, 2), 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(Rational(-2, 3), 2))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(-1, 1))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-1, S.Half))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-1, 2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-2, S.Half))**oo == SetExpr(Interval(-oo, oo))
assert (SetExpr(Interval(1, 2))**x).dummy_eq(SetExpr(ImageSet(Lambda(_d, _d**x), Interval(1, 2))))
assert SetExpr(Interval(2, 3))**(-oo) == SetExpr(FiniteSet(0))
assert SetExpr(Interval(0, 2))**(-oo) == SetExpr(Interval(0, oo))
assert (SetExpr(Interval(-1, 2))**(-oo)).dummy_eq(SetExpr(ImageSet(Lambda(_d, _d**(-oo)), Interval(-1, 2))))
def test_is_strictly_increasing():
"""Test whether is_strictly_increasing returns correct value."""
assert is_strictly_increasing(
4*x**3 - 6*x**2 - 72*x + 30, Interval.Ropen(-oo, -2))
assert is_strictly_increasing(
4*x**3 - 6*x**2 - 72*x + 30, Interval.Lopen(3, oo))
assert not is_strictly_increasing(
4*x**3 - 6*x**2 - 72*x + 30, Interval.open(-2, 3))
assert not is_strictly_increasing(-x**2, Interval(0, oo))
assert not is_strictly_decreasing(1)
def test_SetExpr_Interval_pow():
assert SetExpr(Interval(0, 2))**2 == SetExpr(Interval(0, 4))
assert SetExpr(Interval(-1, 1))**2 == SetExpr(Interval(0, 1))
assert SetExpr(Interval(1, 2))**2 == SetExpr(Interval(1, 4))
assert SetExpr(Interval(-1, 2))**3 == SetExpr(Interval(-1, 8))
assert SetExpr(Interval(-1, 1))**0 == SetExpr(FiniteSet(1))
#assert SetExpr(Interval(1, 2))**(S(5)/2) == SetExpr(Interval(1, 4*sqrt(2)))
#assert SetExpr(Interval(-1, 2))**(S.One/3) == SetExpr(Interval(-1, 2**(S.One/3)))
#assert SetExpr(Interval(0, 2))**(S.One/2) == SetExpr(Interval(0, sqrt(2)))
#assert SetExpr(Interval(-4, 2))**(S(2)/3) == SetExpr(Interval(0, 2*2**(S.One/3)))
#assert SetExpr(Interval(-1, 5))**(S.One/2) == SetExpr(Interval(0, sqrt(5)))
#assert SetExpr(Interval(-oo, 2))**(S.One/2) == SetExpr(Interval(0, sqrt(2)))
#assert SetExpr(Interval(-2, 3))**(S(-1)/4) == SetExpr(Interval(0, oo))
assert SetExpr(Interval(1, 5))**(-2) == SetExpr(Interval(S.One/25, 1))
assert SetExpr(Interval(-1, 3))**(-2) == SetExpr(Interval(0, oo))
assert SetExpr(Interval(0, 2))**(-2) == SetExpr(Interval(S.One/4, oo))
assert SetExpr(Interval(-1, 2))**(-3) == SetExpr(Union(Interval(-oo, -1), Interval(S(1)/8, oo)))
assert SetExpr(Interval(-3, -2))**(-3) == SetExpr(Interval(S(-1)/8, -S.One/27))
assert SetExpr(Interval(-3, -2))**(-2) == SetExpr(Interval(S.One/9, S.One/4))
#assert SetExpr(Interval(0, oo))**(S.One/2) == SetExpr(Interval(0, oo))
#assert SetExpr(Interval(-oo, -1))**(S.One/3) == SetExpr(Interval(-oo, -1))
#assert SetExpr(Interval(-2, 3))**(-S.One/3) == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-oo, 0))**(-2) == SetExpr(Interval.open(0, oo))
assert SetExpr(Interval(-2, 0))**(-2) == SetExpr(Interval(S.One/4, oo))
assert SetExpr(Interval(S.One/3, S.One/2))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(0, S.One/2))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(S.One/2, 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(0, 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(2, 3))**oo == SetExpr(FiniteSet(oo))
assert SetExpr(Interval(1, 2))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(S.One/2, 3))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(-S.One/3, -S.One/4))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(-1, -S.One/2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-3, -2))**oo == SetExpr(FiniteSet(-oo, oo))
assert SetExpr(Interval(-2, -1))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-2, -S.One/2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-S.One/2, S.One/2))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(-S.One/2, 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(-S(2)/3, 2))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(-1, 1))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-1, S.One/2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-1, 2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-2, S.One/2))**oo == SetExpr(Interval(-oo, oo))
assert (SetExpr(Interval(1, 2))**x).dummy_eq(SetExpr(ImageSet(Lambda(_d, _d**x), Interval(1, 2))))
assert SetExpr(Interval(2, 3))**(-oo) == SetExpr(FiniteSet(0))
assert SetExpr(Interval(0, 2))**(-oo) == SetExpr(Interval(0, oo))
assert (SetExpr(Interval(-1, 2))**(-oo)).dummy_eq(SetExpr(ImageSet(Lambda(_d, _d**(-oo)), Interval(-1, 2))))
def solve_univariate_inequality(expr, gen, relational=True, domain=S.Reals, continuous=False):
"""Solves a real univariate inequality.
Parameters
==========
expr : Relational
The target inequality
gen : Symbol
The variable for which the inequality is solved
relational : bool
A Relational type output is expected or not
domain : Set
The domain over which the equation is solved
continuous: bool
True if expr is known to be continuous over the given domain
(and so continuous_domain() doesn't need to be called on it)
Raises
======
NotImplementedError
The solution of the inequality cannot be determined due to limitation
in `solvify`.
Notes
=====
Currently, we cannot solve all the inequalities due to limitations in
`solvify`. Also, the solution returned for trigonometric inequalities
are restricted in its periodic interval.
See Also
========
solvify: solver returning solveset solutions with solve's output API
Examples
========
>>> from sympy.solvers.inequalities import solve_univariate_inequality
>>> from sympy import Symbol, sin, Interval, S
>>> x = Symbol('x')
>>> solve_univariate_inequality(x**2 >= 4, x)
((2 <= x) & (x < oo)) | ((x <= -2) & (-oo < x))
>>> solve_univariate_inequality(x**2 >= 4, x, relational=False)
Union(Interval(-oo, -2), Interval(2, oo))
>>> domain = Interval(0, S.Infinity)
>>> solve_univariate_inequality(x**2 >= 4, x, False, domain)
Interval(2, oo)
>>> solve_univariate_inequality(sin(x) > 0, x, relational=False)
Interval.open(0, pi)
"""
from sympy.calculus.util import (continuous_domain, periodicity,
function_range)
from sympy.solvers.solvers import denoms
from sympy.solvers.solveset import solveset_real, solvify
# This keeps the function independent of the assumptions about `gen`.
# `solveset` makes sure this function is called only when the domain is
# real.
d = Dummy(real=True)
expr = expr.subs(gen, d)
_gen = gen
gen = d
rv = None
if expr is S.true:
rv = domain
elif expr is S.false:
rv = S.EmptySet
else:
e = expr.lhs - expr.rhs
period = periodicity(e, gen)
if period is not None:
frange = function_range(e, gen, domain)
rel = expr.rel_op
if rel == '<' or rel == '<=':
if expr.func(frange.sup, 0):
rv = domain
elif not expr.func(frange.inf, 0):
rv = S.EmptySet
elif rel == '>' or rel == '>=':
if expr.func(frange.inf, 0):
rv = domain
elif not expr.func(frange.sup, 0):
rv = S.EmptySet
inf, sup = domain.inf, domain.sup
if sup - inf is S.Infinity:
domain = Interval(0, period, False, True)
if rv is None:
solns = solvify(e, gen, domain)
if solns is None:
raise NotImplementedError(filldedent('''The inequality cannot be
solved using solve_univariate_inequality.'''))
singularities = []
for d in denoms(expr, gen):
singularities.extend(solvify(d, gen, domain))
if not continuous:
domain = continuous_domain(e, gen, domain)
include_x = expr.func(0, 0)
def valid(x):
v = e.subs(gen, x)
try:
r = expr.func(v, 0)
except TypeError:
r = S.false
if r in (S.true, S.false):
return r
if v.is_real is False:
return S.false
else:
v = v.n(2)
if v.is_comparable:
return expr.func(v, 0)
return S.false
try:
discontinuities = set(domain.boundary -
FiniteSet(domain.inf, domain.sup))
# remove points that are not between inf and sup of domain
critical_points = FiniteSet(*(solns + singularities + list(
discontinuities))).intersection(
Interval(domain.inf, domain.sup,
domain.inf not in domain, domain.sup not in domain))
reals = _nsort(critical_points, separated=True)[0]
except NotImplementedError:
raise NotImplementedError('sorting of these roots is not supported')
sol_sets = [S.EmptySet]
start = domain.inf
if valid(start) and start.is_finite:
sol_sets.append(FiniteSet(start))
for x in reals:
end = x
if valid(_pt(start, end)):
sol_sets.append(Interval(start, end, True, True))
if x in singularities:
singularities.remove(x)
else:
if x in discontinuities:
discontinuities.remove(x)
_valid = valid(x)
else: # it's a solution
_valid = include_x
if _valid:
sol_sets.append(FiniteSet(x))
start = end
end = domain.sup
if valid(end) and end.is_finite:
sol_sets.append(FiniteSet(end))
if valid(_pt(start, end)):
sol_sets.append(Interval.open(start, end))
rv = Union(*sol_sets).subs(gen, _gen)
return rv if not relational else rv.as_relational(_gen)
def test_strictly_decreasing():
assert is_strictly_decreasing(1/(x**2 - 3*x), Interval.open(1.5, 3))
def solve_univariate_inequality(expr,
gen,
relational=True,
domain=S.Reals,
continuous=False):
"""Solves a real univariate inequality.
Parameters
==========
expr : Relational
The target inequality
gen : Symbol
The variable for which the inequality is solved
relational : bool
A Relational type output is expected or not
domain : Set
The domain over which the equation is solved
continuous: bool
True if expr is known to be continuous over the given domain
(and so continuous_domain() doesn't need to be called on it)
Raises
======
NotImplementedError
The solution of the inequality cannot be determined due to limitation
in `solvify`.
Notes
=====
Currently, we cannot solve all the inequalities due to limitations in
`solvify`. Also, the solution returned for trigonometric inequalities
are restricted in its periodic interval.
See Also
========
solvify: solver returning solveset solutions with solve's output API
Examples
========
>>> from sympy.solvers.inequalities import solve_univariate_inequality
>>> from sympy import Symbol, sin, Interval, S
>>> x = Symbol('x')
>>> solve_univariate_inequality(x**2 >= 4, x)
((2 <= x) & (x < oo)) | ((x <= -2) & (-oo < x))
>>> solve_univariate_inequality(x**2 >= 4, x, relational=False)
Union(Interval(-oo, -2, True), Interval(2, oo, False, True))
>>> domain = Interval(0, S.Infinity)
>>> solve_univariate_inequality(x**2 >= 4, x, False, domain)
Interval(2, oo, False, True)
>>> solve_univariate_inequality(sin(x) > 0, x, relational=False)
Interval(0, pi, True, True)
"""
from sympy.calculus.util import (continuous_domain, periodicity,
function_range)
from sympy.solvers.solvers import denoms
from sympy.solvers.solveset import solveset_real, solvify
# This keeps the function independent of the assumptions about `gen`.
# `solveset` makes sure this function is called only when the domain is
# real.
d = Dummy(real=True)
expr = expr.subs(gen, d)
_gen = gen
gen = d
rv = None
if expr is S.true:
rv = domain
elif expr is S.false:
rv = S.EmptySet
else:
e = expr.lhs - expr.rhs
period = periodicity(e, gen)
if period is not None:
frange = function_range(e, gen, domain)
rel = expr.rel_op
if rel == '<' or rel == '<=':
if expr.func(frange.sup, 0):
rv = domain
elif not expr.func(frange.inf, 0):
rv = S.EmptySet
elif rel == '>' or rel == '>=':
if expr.func(frange.inf, 0):
rv = domain
elif not expr.func(frange.sup, 0):
rv = S.EmptySet
inf, sup = domain.inf, domain.sup
if sup - inf is S.Infinity:
domain = Interval(0, period, False, True)
if rv is None:
solns = solvify(e, gen, domain)
if solns is None:
raise NotImplementedError(
filldedent('''The inequality cannot be
solved using solve_univariate_inequality.'''))
singularities = []
for d in denoms(expr, gen):
singularities.extend(solvify(d, gen, domain))
if not continuous:
domain = continuous_domain(e, gen, domain)
include_x = expr.func(0, 0)
def valid(x):
v = e.subs(gen, x)
try:
r = expr.func(v, 0)
except TypeError:
r = S.false
if r in (S.true, S.false):
return r
if v.is_real is False:
return S.false
else:
v = v.n(2)
if v.is_comparable:
return expr.func(v, 0)
return S.false
try:
discontinuities = set(domain.boundary -
FiniteSet(domain.inf, domain.sup))
# remove points that are not between inf and sup of domain
critical_points = FiniteSet(
*(solns + singularities +
list(discontinuities))).intersection(
Interval(domain.inf, domain.sup, domain.inf
not in domain, domain.sup not in domain))
reals = _nsort(critical_points, separated=True)[0]
except NotImplementedError:
raise NotImplementedError(
'sorting of these roots is not supported')
sol_sets = [S.EmptySet]
start = domain.inf
if valid(start) and start.is_finite:
sol_sets.append(FiniteSet(start))
for x in reals:
end = x
if valid(_pt(start, end)):
sol_sets.append(Interval(start, end, True, True))
if x in singularities:
singularities.remove(x)
else:
if x in discontinuities:
discontinuities.remove(x)
_valid = valid(x)
else: # it's a solution
_valid = include_x
if _valid:
sol_sets.append(FiniteSet(x))
start = end
end = domain.sup
if valid(end) and end.is_finite:
sol_sets.append(FiniteSet(end))
if valid(_pt(start, end)):
sol_sets.append(Interval.open(start, end))
rv = Union(*sol_sets).subs(gen, _gen)
return rv if not relational else rv.as_relational(_gen)
def test_strictly_decreasing():
assert is_strictly_decreasing(1 / (x**2 - 3 * x), Interval.open(1.5, 3))
def test_is_monotonic():
assert is_monotonic(1 / (x**2 - 3 * x), Interval.open(1.5, 3))
assert is_monotonic(1 / (x**2 - 3 * x), Interval.Lopen(3, oo))
assert is_monotonic(x**3 - 3 * x**2 + 4 * x, S.Reals)
assert is_monotonic(-x**2, S.Reals) is False
assert is_monotonic(x**2 + y + 1, Interval(1, 2), x) is True
def test_is_strictly_increasing():
assert is_strictly_increasing(4*x**3 - 6*x**2 - 72*x + 30, Interval.Ropen(-oo, -2))
assert is_strictly_increasing(4*x**3 - 6*x**2 - 72*x + 30, Interval.Lopen(3, oo))
assert is_strictly_increasing(4*x**3 - 6*x**2 - 72*x + 30, Interval.open(-2, 3)) is False
assert is_strictly_increasing(-x**2, Interval(0, oo)) is False
def test_Interval_arithmetic():
i12cc = SetExpr(Interval(1, 2))
i12lo = SetExpr(Interval.Lopen(1, 2))
i12ro = SetExpr(Interval.Ropen(1, 2))
i12o = SetExpr(Interval.open(1, 2))
n23cc = SetExpr(Interval(-2, 3))
n23lo = SetExpr(Interval.Lopen(-2, 3))
n23ro = SetExpr(Interval.Ropen(-2, 3))
n23o = SetExpr(Interval.open(-2, 3))
n3n2cc = SetExpr(Interval(-3, -2))
assert i12cc + i12cc == SetExpr(Interval(2, 4))
assert i12cc - i12cc == SetExpr(Interval(-1, 1))
assert i12cc * i12cc == SetExpr(Interval(1, 4))
assert i12cc / i12cc == SetExpr(Interval(S.Half, 2))
assert i12cc ** 2 == SetExpr(Interval(1, 4))
assert i12cc ** 3 == SetExpr(Interval(1, 8))
assert i12lo + i12ro == SetExpr(Interval.open(2, 4))
assert i12lo - i12ro == SetExpr(Interval.Lopen(-1, 1))
assert i12lo * i12ro == SetExpr(Interval.open(1, 4))
assert i12lo / i12ro == SetExpr(Interval.Lopen(S.Half, 2))
assert i12lo + i12lo == SetExpr(Interval.Lopen(2, 4))
assert i12lo - i12lo == SetExpr(Interval.open(-1, 1))
assert i12lo * i12lo == SetExpr(Interval.Lopen(1, 4))
assert i12lo / i12lo == SetExpr(Interval.open(S.Half, 2))
assert i12lo + i12cc == SetExpr(Interval.Lopen(2, 4))
assert i12lo - i12cc == SetExpr(Interval.Lopen(-1, 1))
assert i12lo * i12cc == SetExpr(Interval.Lopen(1, 4))
assert i12lo / i12cc == SetExpr(Interval.Lopen(S.Half, 2))
assert i12lo + i12o == SetExpr(Interval.open(2, 4))
assert i12lo - i12o == SetExpr(Interval.open(-1, 1))
assert i12lo * i12o == SetExpr(Interval.open(1, 4))
assert i12lo / i12o == SetExpr(Interval.open(S.Half, 2))
assert i12lo ** 2 == SetExpr(Interval.Lopen(1, 4))
assert i12lo ** 3 == SetExpr(Interval.Lopen(1, 8))
assert i12ro + i12ro == SetExpr(Interval.Ropen(2, 4))
assert i12ro - i12ro == SetExpr(Interval.open(-1, 1))
assert i12ro * i12ro == SetExpr(Interval.Ropen(1, 4))
assert i12ro / i12ro == SetExpr(Interval.open(S.Half, 2))
assert i12ro + i12cc == SetExpr(Interval.Ropen(2, 4))
assert i12ro - i12cc == SetExpr(Interval.Ropen(-1, 1))
assert i12ro * i12cc == SetExpr(Interval.Ropen(1, 4))
assert i12ro / i12cc == SetExpr(Interval.Ropen(S.Half, 2))
assert i12ro + i12o == SetExpr(Interval.open(2, 4))
assert i12ro - i12o == SetExpr(Interval.open(-1, 1))
assert i12ro * i12o == SetExpr(Interval.open(1, 4))
assert i12ro / i12o == SetExpr(Interval.open(S.Half, 2))
assert i12ro ** 2 == SetExpr(Interval.Ropen(1, 4))
assert i12ro ** 3 == SetExpr(Interval.Ropen(1, 8))
assert i12o + i12lo == SetExpr(Interval.open(2, 4))
assert i12o - i12lo == SetExpr(Interval.open(-1, 1))
assert i12o * i12lo == SetExpr(Interval.open(1, 4))
assert i12o / i12lo == SetExpr(Interval.open(S.Half, 2))
assert i12o + i12ro == SetExpr(Interval.open(2, 4))
assert i12o - i12ro == SetExpr(Interval.open(-1, 1))
assert i12o * i12ro == SetExpr(Interval.open(1, 4))
assert i12o / i12ro == SetExpr(Interval.open(S.Half, 2))
assert i12o + i12cc == SetExpr(Interval.open(2, 4))
assert i12o - i12cc == SetExpr(Interval.open(-1, 1))
assert i12o * i12cc == SetExpr(Interval.open(1, 4))
assert i12o / i12cc == SetExpr(Interval.open(S.Half, 2))
assert i12o ** 2 == SetExpr(Interval.open(1, 4))
assert i12o ** 3 == SetExpr(Interval.open(1, 8))
assert n23cc + n23cc == SetExpr(Interval(-4, 6))
assert n23cc - n23cc == SetExpr(Interval(-5, 5))
assert n23cc * n23cc == SetExpr(Interval(-6, 9))
assert n23cc / n23cc == SetExpr(Interval.open(-oo, oo))
assert n23cc + n23ro == SetExpr(Interval.Ropen(-4, 6))
assert n23cc - n23ro == SetExpr(Interval.Lopen(-5, 5))
assert n23cc * n23ro == SetExpr(Interval.Ropen(-6, 9))
assert n23cc / n23ro == SetExpr(Interval.Lopen(-oo, oo))
assert n23cc + n23lo == SetExpr(Interval.Lopen(-4, 6))
assert n23cc - n23lo == SetExpr(Interval.Ropen(-5, 5))
assert n23cc * n23lo == SetExpr(Interval(-6, 9))
assert n23cc / n23lo == SetExpr(Interval.open(-oo, oo))
assert n23cc + n23o == SetExpr(Interval.open(-4, 6))
assert n23cc - n23o == SetExpr(Interval.open(-5, 5))
assert n23cc * n23o == SetExpr(Interval.open(-6, 9))
assert n23cc / n23o == SetExpr(Interval.open(-oo, oo))
assert n23cc ** 2 == SetExpr(Interval(0, 9))
assert n23cc ** 3 == SetExpr(Interval(-8, 27))
n32cc = SetExpr(Interval(-3, 2))
n32lo = SetExpr(Interval.Lopen(-3, 2))
n32ro = SetExpr(Interval.Ropen(-3, 2))
assert n32cc * n32lo == SetExpr(Interval.Ropen(-6, 9))
assert n32cc * n32cc == SetExpr(Interval(-6, 9))
assert n32lo * n32cc == SetExpr(Interval.Ropen(-6, 9))
assert n32cc * n32ro == SetExpr(Interval(-6, 9))
assert n32lo * n32ro == SetExpr(Interval.Ropen(-6, 9))
assert n32cc / n32lo == SetExpr(Interval.Ropen(-oo, oo))
assert i12cc / n32lo == SetExpr(Interval.Ropen(-oo, oo))
assert n3n2cc ** 2 == SetExpr(Interval(4, 9))
assert n3n2cc ** 3 == SetExpr(Interval(-27, -8))
assert n23cc + i12cc == SetExpr(Interval(-1, 5))
assert n23cc - i12cc == SetExpr(Interval(-4, 2))
assert n23cc * i12cc == SetExpr(Interval(-4, 6))
assert n23cc / i12cc == SetExpr(Interval(-2, 3))
def test_is_strictly_decreasing():
assert is_decreasing(1/(x**2 - 3*x), Interval.open(1.5, 3))
assert is_decreasing(1/(x**2 - 3*x), Interval.Lopen(3, oo))
assert is_decreasing(1/(x**2 - 3*x), Interval.Ropen(-oo, S(3)/2)) is False
assert is_decreasing(-x**2, Interval(-oo, 0)) is False
def solve_univariate_inequality(expr, gen, relational=True, domain=S.Reals, continuous=False):
"""Solves a real univariate inequality.
Parameters
==========
expr : Relational
The target inequality
gen : Symbol
The variable for which the inequality is solved
relational : bool
A Relational type output is expected or not
domain : Set
The domain over which the equation is solved
continuous: bool
True if expr is known to be continuous over the given domain
(and so continuous_domain() doesn't need to be called on it)
Raises
======
NotImplementedError
The solution of the inequality cannot be determined due to limitation
in `solvify`.
Notes
=====
Currently, we cannot solve all the inequalities due to limitations in
`solvify`. Also, the solution returned for trigonometric inequalities
are restricted in its periodic interval.
See Also
========
solvify: solver returning solveset solutions with solve's output API
Examples
========
>>> from sympy.solvers.inequalities import solve_univariate_inequality
>>> from sympy import Symbol, sin, Interval, S
>>> x = Symbol('x')
>>> solve_univariate_inequality(x**2 >= 4, x)
((2 <= x) & (x < oo)) | ((x <= -2) & (-oo < x))
>>> solve_univariate_inequality(x**2 >= 4, x, relational=False)
Union(Interval(-oo, -2), Interval(2, oo))
>>> domain = Interval(0, S.Infinity)
>>> solve_univariate_inequality(x**2 >= 4, x, False, domain)
Interval(2, oo)
>>> solve_univariate_inequality(sin(x) > 0, x, relational=False)
Interval.open(0, pi)
"""
from sympy import im
from sympy.calculus.util import (continuous_domain, periodicity,
function_range)
from sympy.solvers.solvers import denoms
from sympy.solvers.solveset import solveset_real, solvify, solveset
from sympy.solvers.solvers import solve
# This keeps the function independent of the assumptions about `gen`.
# `solveset` makes sure this function is called only when the domain is
# real.
_gen = gen
_domain = domain
if gen.is_real is False:
rv = S.EmptySet
return rv if not relational else rv.as_relational(_gen)
elif gen.is_real is None:
gen = Dummy('gen', real=True)
try:
expr = expr.xreplace({_gen: gen})
except TypeError:
raise TypeError(filldedent('''
When gen is real, the relational has a complex part
which leads to an invalid comparison like I < 0.
'''))
rv = None
if expr is S.true:
rv = domain
elif expr is S.false:
rv = S.EmptySet
else:
e = expr.lhs - expr.rhs
period = periodicity(e, gen)
if period is not None:
frange = function_range(e, gen, domain)
rel = expr.rel_op
if rel == '<' or rel == '<=':
if expr.func(frange.sup, 0):
rv = domain
elif not expr.func(frange.inf, 0):
rv = S.EmptySet
elif rel == '>' or rel == '>=':
if expr.func(frange.inf, 0):
rv = domain
elif not expr.func(frange.sup, 0):
rv = S.EmptySet
inf, sup = domain.inf, domain.sup
if sup - inf is S.Infinity:
domain = Interval(0, period, False, True)
if rv is None:
n, d = e.as_numer_denom()
try:
if gen not in n.free_symbols and len(e.free_symbols) > 1:
raise ValueError
# this might raise ValueError on its own
# or it might give None...
solns = solvify(e, gen, domain)
if solns is None:
# in which case we raise ValueError
raise ValueError
except (ValueError, NotImplementedError):
raise NotImplementedError(filldedent('''
The inequality cannot be solved using solve_univariate_inequality.
'''))
expanded_e = expand_mul(e)
def valid(x):
# this is used to see if gen=x satisfies the
# relational by substituting it into the
# expanded form and testing against 0, e.g.
# if expr = x*(x + 1) < 2 then e = x*(x + 1) - 2
# and expanded_e = x**2 + x - 2; the test is
# whether a given value of x satisfies
# x**2 + x - 2 < 0
#
# expanded_e, expr and gen used from enclosing scope
v = expanded_e.subs(gen, x)
try:
r = expr.func(v, 0)
except TypeError:
r = S.false
if r in (S.true, S.false):
return r
if v.is_real is False:
return S.false
else:
v = v.n(2)
if v.is_comparable:
return expr.func(v, 0)
# not comparable or couldn't be evaluated
raise NotImplementedError(
'relationship did not evaluate: %s' % r)
singularities = []
for d in denoms(expr, gen):
singularities.extend(solvify(d, gen, domain))
if not continuous:
domain = continuous_domain(e, gen, domain)
include_x = '=' in expr.rel_op and expr.rel_op != '!='
try:
discontinuities = set(domain.boundary -
FiniteSet(domain.inf, domain.sup))
# remove points that are not between inf and sup of domain
critical_points = FiniteSet(*(solns + singularities + list(
discontinuities))).intersection(
Interval(domain.inf, domain.sup,
domain.inf not in domain, domain.sup not in domain))
if all(r.is_number for r in critical_points):
reals = _nsort(critical_points, separated=True)[0]
else:
from sympy.utilities.iterables import sift
sifted = sift(critical_points, lambda x: x.is_real)
if sifted[None]:
# there were some roots that weren't known
# to be real
raise NotImplementedError
try:
reals = sifted[True]
if len(reals) > 1:
reals = list(sorted(reals))
except TypeError:
raise NotImplementedError
except NotImplementedError:
raise NotImplementedError('sorting of these roots is not supported')
#If expr contains imaginary coefficients
#Only real values of x for which the imaginary part is 0 are taken
make_real = S.Reals
if im(expanded_e) != S.Zero:
check = True
im_sol = FiniteSet()
try:
a = solveset(im(expanded_e), gen, domain)
if not isinstance(a, Interval):
for z in a:
if z not in singularities and valid(z) and z.is_real:
im_sol += FiniteSet(z)
else:
start, end = a.inf, a.sup
for z in _nsort(critical_points + FiniteSet(end)):
valid_start = valid(start)
if start != end:
valid_z = valid(z)
pt = _pt(start, z)
if pt not in singularities and pt.is_real and valid(pt):
if valid_start and valid_z:
im_sol += Interval(start, z)
elif valid_start:
im_sol += Interval.Ropen(start, z)
elif valid_z:
im_sol += Interval.Lopen(start, z)
else:
im_sol += Interval.open(start, z)
start = z
for s in singularities:
im_sol -= FiniteSet(s)
except (TypeError):
im_sol = S.Reals
check = False
if isinstance(im_sol, EmptySet):
raise ValueError(filldedent('''
%s contains imaginary parts which cannot be made 0 for any value of %s
satisfying the inequality, leading to relations like I < 0.
''' % (expr.subs(gen, _gen), _gen)))
make_real = make_real.intersect(im_sol)
empty = sol_sets = [S.EmptySet]
start = domain.inf
if valid(start) and start.is_finite:
sol_sets.append(FiniteSet(start))
for x in reals:
end = x
if valid(_pt(start, end)):
sol_sets.append(Interval(start, end, True, True))
if x in singularities:
singularities.remove(x)
else:
if x in discontinuities:
discontinuities.remove(x)
_valid = valid(x)
else: # it's a solution
_valid = include_x
if _valid:
sol_sets.append(FiniteSet(x))
start = end
end = domain.sup
if valid(end) and end.is_finite:
sol_sets.append(FiniteSet(end))
if valid(_pt(start, end)):
sol_sets.append(Interval.open(start, end))
if im(expanded_e) != S.Zero and check:
rv = (make_real).intersect(_domain)
else:
rv = Intersection(
(Union(*sol_sets)), make_real, _domain).subs(gen, _gen)
return rv if not relational else rv.as_relational(_gen)
def test_is_monotonic():
assert is_monotonic(1/(x**2 - 3*x), Interval.open(1.5, 3))
assert is_monotonic(1/(x**2 - 3*x), Interval.Lopen(3, oo))
assert is_monotonic(x**3 - 3*x**2 + 4*x, S.Reals)
assert is_monotonic(-x**2, S.Reals) is False
def test_Interval_arithmetic():
i12cc = SetExpr(Interval(1, 2))
i12lo = SetExpr(Interval.Lopen(1, 2))
i12ro = SetExpr(Interval.Ropen(1, 2))
i12o = SetExpr(Interval.open(1, 2))
n23cc = SetExpr(Interval(-2, 3))
n23lo = SetExpr(Interval.Lopen(-2, 3))
n23ro = SetExpr(Interval.Ropen(-2, 3))
n23o = SetExpr(Interval.open(-2, 3))
n3n2cc = SetExpr(Interval(-3, -2))
assert i12cc + i12cc == SetExpr(Interval(2, 4))
assert i12cc - i12cc == SetExpr(Interval(-1, 1))
assert i12cc * i12cc == SetExpr(Interval(1, 4))
assert i12cc / i12cc == SetExpr(Interval(S.Half, 2))
assert i12cc**2 == SetExpr(Interval(1, 4))
assert i12cc**3 == SetExpr(Interval(1, 8))
assert i12lo + i12ro == SetExpr(Interval.open(2, 4))
assert i12lo - i12ro == SetExpr(Interval.Lopen(-1, 1))
assert i12lo * i12ro == SetExpr(Interval.open(1, 4))
assert i12lo / i12ro == SetExpr(Interval.Lopen(S.Half, 2))
assert i12lo + i12lo == SetExpr(Interval.Lopen(2, 4))
assert i12lo - i12lo == SetExpr(Interval.open(-1, 1))
assert i12lo * i12lo == SetExpr(Interval.Lopen(1, 4))
assert i12lo / i12lo == SetExpr(Interval.open(S.Half, 2))
assert i12lo + i12cc == SetExpr(Interval.Lopen(2, 4))
assert i12lo - i12cc == SetExpr(Interval.Lopen(-1, 1))
assert i12lo * i12cc == SetExpr(Interval.Lopen(1, 4))
assert i12lo / i12cc == SetExpr(Interval.Lopen(S.Half, 2))
assert i12lo + i12o == SetExpr(Interval.open(2, 4))
assert i12lo - i12o == SetExpr(Interval.open(-1, 1))
assert i12lo * i12o == SetExpr(Interval.open(1, 4))
assert i12lo / i12o == SetExpr(Interval.open(S.Half, 2))
assert i12lo**2 == SetExpr(Interval.Lopen(1, 4))
assert i12lo**3 == SetExpr(Interval.Lopen(1, 8))
assert i12ro + i12ro == SetExpr(Interval.Ropen(2, 4))
assert i12ro - i12ro == SetExpr(Interval.open(-1, 1))
assert i12ro * i12ro == SetExpr(Interval.Ropen(1, 4))
assert i12ro / i12ro == SetExpr(Interval.open(S.Half, 2))
assert i12ro + i12cc == SetExpr(Interval.Ropen(2, 4))
assert i12ro - i12cc == SetExpr(Interval.Ropen(-1, 1))
assert i12ro * i12cc == SetExpr(Interval.Ropen(1, 4))
assert i12ro / i12cc == SetExpr(Interval.Ropen(S.Half, 2))
assert i12ro + i12o == SetExpr(Interval.open(2, 4))
assert i12ro - i12o == SetExpr(Interval.open(-1, 1))
assert i12ro * i12o == SetExpr(Interval.open(1, 4))
assert i12ro / i12o == SetExpr(Interval.open(S.Half, 2))
assert i12ro**2 == SetExpr(Interval.Ropen(1, 4))
assert i12ro**3 == SetExpr(Interval.Ropen(1, 8))
assert i12o + i12lo == SetExpr(Interval.open(2, 4))
assert i12o - i12lo == SetExpr(Interval.open(-1, 1))
assert i12o * i12lo == SetExpr(Interval.open(1, 4))
assert i12o / i12lo == SetExpr(Interval.open(S.Half, 2))
assert i12o + i12ro == SetExpr(Interval.open(2, 4))
assert i12o - i12ro == SetExpr(Interval.open(-1, 1))
assert i12o * i12ro == SetExpr(Interval.open(1, 4))
assert i12o / i12ro == SetExpr(Interval.open(S.Half, 2))
assert i12o + i12cc == SetExpr(Interval.open(2, 4))
assert i12o - i12cc == SetExpr(Interval.open(-1, 1))
assert i12o * i12cc == SetExpr(Interval.open(1, 4))
assert i12o / i12cc == SetExpr(Interval.open(S.Half, 2))
assert i12o**2 == SetExpr(Interval.open(1, 4))
assert i12o**3 == SetExpr(Interval.open(1, 8))
assert n23cc + n23cc == SetExpr(Interval(-4, 6))
assert n23cc - n23cc == SetExpr(Interval(-5, 5))
assert n23cc * n23cc == SetExpr(Interval(-6, 9))
assert n23cc / n23cc == SetExpr(Interval.open(-oo, oo))
assert n23cc + n23ro == SetExpr(Interval.Ropen(-4, 6))
assert n23cc - n23ro == SetExpr(Interval.Lopen(-5, 5))
assert n23cc * n23ro == SetExpr(Interval.Ropen(-6, 9))
assert n23cc / n23ro == SetExpr(Interval.Lopen(-oo, oo))
assert n23cc + n23lo == SetExpr(Interval.Lopen(-4, 6))
assert n23cc - n23lo == SetExpr(Interval.Ropen(-5, 5))
assert n23cc * n23lo == SetExpr(Interval(-6, 9))
assert n23cc / n23lo == SetExpr(Interval.open(-oo, oo))
assert n23cc + n23o == SetExpr(Interval.open(-4, 6))
assert n23cc - n23o == SetExpr(Interval.open(-5, 5))
assert n23cc * n23o == SetExpr(Interval.open(-6, 9))
assert n23cc / n23o == SetExpr(Interval.open(-oo, oo))
assert n23cc**2 == SetExpr(Interval(0, 9))
assert n23cc**3 == SetExpr(Interval(-8, 27))
n32cc = SetExpr(Interval(-3, 2))
n32lo = SetExpr(Interval.Lopen(-3, 2))
n32ro = SetExpr(Interval.Ropen(-3, 2))
assert n32cc * n32lo == SetExpr(Interval.Ropen(-6, 9))
assert n32cc * n32cc == SetExpr(Interval(-6, 9))
assert n32lo * n32cc == SetExpr(Interval.Ropen(-6, 9))
assert n32cc * n32ro == SetExpr(Interval(-6, 9))
assert n32lo * n32ro == SetExpr(Interval.Ropen(-6, 9))
assert n32cc / n32lo == SetExpr(Interval.Ropen(-oo, oo))
assert i12cc / n32lo == SetExpr(Interval.Ropen(-oo, oo))
assert n3n2cc**2 == SetExpr(Interval(4, 9))
assert n3n2cc**3 == SetExpr(Interval(-27, -8))
assert n23cc + i12cc == SetExpr(Interval(-1, 5))
assert n23cc - i12cc == SetExpr(Interval(-4, 2))
assert n23cc * i12cc == SetExpr(Interval(-4, 6))
assert n23cc / i12cc == SetExpr(Interval(-2, 3))
def solve_univariate_inequality(expr,
gen,
relational=True,
domain=S.Reals,
continuous=False):
"""Solves a real univariate inequality.
Parameters
==========
expr : Relational
The target inequality
gen : Symbol
The variable for which the inequality is solved
relational : bool
A Relational type output is expected or not
domain : Set
The domain over which the equation is solved
continuous: bool
True if expr is known to be continuous over the given domain
(and so continuous_domain() doesn't need to be called on it)
Raises
======
NotImplementedError
The solution of the inequality cannot be determined due to limitation
in `solvify`.
Notes
=====
Currently, we cannot solve all the inequalities due to limitations in
`solvify`. Also, the solution returned for trigonometric inequalities
are restricted in its periodic interval.
See Also
========
solvify: solver returning solveset solutions with solve's output API
Examples
========
>>> from sympy.solvers.inequalities import solve_univariate_inequality
>>> from sympy import Symbol, sin, Interval, S
>>> x = Symbol('x')
>>> solve_univariate_inequality(x**2 >= 4, x)
((2 <= x) & (x < oo)) | ((x <= -2) & (-oo < x))
>>> solve_univariate_inequality(x**2 >= 4, x, relational=False)
Union(Interval(-oo, -2), Interval(2, oo))
>>> domain = Interval(0, S.Infinity)
>>> solve_univariate_inequality(x**2 >= 4, x, False, domain)
Interval(2, oo)
>>> solve_univariate_inequality(sin(x) > 0, x, relational=False)
Interval.open(0, pi)
"""
from sympy import im
from sympy.calculus.util import (continuous_domain, periodicity,
function_range)
from sympy.solvers.solvers import denoms
from sympy.solvers.solveset import solveset_real, solvify, solveset
from sympy.solvers.solvers import solve
# This keeps the function independent of the assumptions about `gen`.
# `solveset` makes sure this function is called only when the domain is
# real.
_gen = gen
_domain = domain
if gen.is_real is False:
rv = S.EmptySet
return rv if not relational else rv.as_relational(_gen)
elif gen.is_real is None:
gen = Dummy('gen', real=True)
try:
expr = expr.xreplace({_gen: gen})
except TypeError:
raise TypeError(
filldedent('''
When gen is real, the relational has a complex part
which leads to an invalid comparison like I < 0.
'''))
rv = None
if expr is S.true:
rv = domain
elif expr is S.false:
rv = S.EmptySet
else:
e = expr.lhs - expr.rhs
period = periodicity(e, gen)
if period is S.Zero:
e = expand_mul(e)
const = expr.func(e, 0)
if const is S.true:
rv = domain
elif const is S.false:
rv = S.EmptySet
elif period is not None:
frange = function_range(e, gen, domain)
rel = expr.rel_op
if rel == '<' or rel == '<=':
if expr.func(frange.sup, 0):
rv = domain
elif not expr.func(frange.inf, 0):
rv = S.EmptySet
elif rel == '>' or rel == '>=':
if expr.func(frange.inf, 0):
rv = domain
elif not expr.func(frange.sup, 0):
rv = S.EmptySet
inf, sup = domain.inf, domain.sup
if sup - inf is S.Infinity:
domain = Interval(0, period, False, True)
if rv is None:
n, d = e.as_numer_denom()
try:
if gen not in n.free_symbols and len(e.free_symbols) > 1:
raise ValueError
# this might raise ValueError on its own
# or it might give None...
solns = solvify(e, gen, domain)
if solns is None:
# in which case we raise ValueError
raise ValueError
except (ValueError, NotImplementedError):
# replace gen with generic x since it's
# univariate anyway
raise NotImplementedError(
filldedent('''
The inequality, %s, cannot be solved using
solve_univariate_inequality.
''' % expr.subs(gen, Symbol('x'))))
expanded_e = expand_mul(e)
def valid(x):
# this is used to see if gen=x satisfies the
# relational by substituting it into the
# expanded form and testing against 0, e.g.
# if expr = x*(x + 1) < 2 then e = x*(x + 1) - 2
# and expanded_e = x**2 + x - 2; the test is
# whether a given value of x satisfies
# x**2 + x - 2 < 0
#
# expanded_e, expr and gen used from enclosing scope
v = expanded_e.subs(gen, expand_mul(x))
try:
r = expr.func(v, 0)
except TypeError:
r = S.false
if r in (S.true, S.false):
return r
if v.is_real is False:
return S.false
else:
v = v.n(2)
if v.is_comparable:
return expr.func(v, 0)
# not comparable or couldn't be evaluated
raise NotImplementedError(
'relationship did not evaluate: %s' % r)
singularities = []
for d in denoms(expr, gen):
singularities.extend(solvify(d, gen, domain))
if not continuous:
domain = continuous_domain(expanded_e, gen, domain)
include_x = '=' in expr.rel_op and expr.rel_op != '!='
try:
discontinuities = set(domain.boundary -
FiniteSet(domain.inf, domain.sup))
# remove points that are not between inf and sup of domain
critical_points = FiniteSet(
*(solns + singularities +
list(discontinuities))).intersection(
Interval(domain.inf, domain.sup, domain.inf
not in domain, domain.sup not in domain))
if all(r.is_number for r in critical_points):
reals = _nsort(critical_points, separated=True)[0]
else:
from sympy.utilities.iterables import sift
sifted = sift(critical_points, lambda x: x.is_real)
if sifted[None]:
# there were some roots that weren't known
# to be real
raise NotImplementedError
try:
reals = sifted[True]
if len(reals) > 1:
reals = list(sorted(reals))
except TypeError:
raise NotImplementedError
except NotImplementedError:
raise NotImplementedError(
'sorting of these roots is not supported')
# If expr contains imaginary coefficients, only take real
# values of x for which the imaginary part is 0
make_real = S.Reals
if im(expanded_e) != S.Zero:
check = True
im_sol = FiniteSet()
try:
a = solveset(im(expanded_e), gen, domain)
if not isinstance(a, Interval):
for z in a:
if z not in singularities and valid(
z) and z.is_real:
im_sol += FiniteSet(z)
else:
start, end = a.inf, a.sup
for z in _nsort(critical_points + FiniteSet(end)):
valid_start = valid(start)
if start != end:
valid_z = valid(z)
pt = _pt(start, z)
if pt not in singularities and pt.is_real and valid(
pt):
if valid_start and valid_z:
im_sol += Interval(start, z)
elif valid_start:
im_sol += Interval.Ropen(start, z)
elif valid_z:
im_sol += Interval.Lopen(start, z)
else:
im_sol += Interval.open(start, z)
start = z
for s in singularities:
im_sol -= FiniteSet(s)
except (TypeError):
im_sol = S.Reals
check = False
if isinstance(im_sol, EmptySet):
raise ValueError(
filldedent('''
%s contains imaginary parts which cannot be
made 0 for any value of %s satisfying the
inequality, leading to relations like I < 0.
''' % (expr.subs(gen, _gen), _gen)))
make_real = make_real.intersect(im_sol)
empty = sol_sets = [S.EmptySet]
start = domain.inf
if valid(start) and start.is_finite:
sol_sets.append(FiniteSet(start))
for x in reals:
end = x
if valid(_pt(start, end)):
sol_sets.append(Interval(start, end, True, True))
if x in singularities:
singularities.remove(x)
else:
if x in discontinuities:
discontinuities.remove(x)
_valid = valid(x)
else: # it's a solution
_valid = include_x
if _valid:
sol_sets.append(FiniteSet(x))
start = end
end = domain.sup
if valid(end) and end.is_finite:
sol_sets.append(FiniteSet(end))
if valid(_pt(start, end)):
sol_sets.append(Interval.open(start, end))
if im(expanded_e) != S.Zero and check:
rv = (make_real).intersect(_domain)
else:
rv = Intersection((Union(*sol_sets)), make_real,
_domain).subs(gen, _gen)
return rv if not relational else rv.as_relational(_gen)
def test_SetExpr_Interval_pow():
assert SetExpr(Interval(0, 2))**2 == SetExpr(Interval(0, 4))
assert SetExpr(Interval(-1, 1))**2 == SetExpr(Interval(0, 1))
assert SetExpr(Interval(1, 2))**2 == SetExpr(Interval(1, 4))
assert SetExpr(Interval(-1, 2))**3 == SetExpr(Interval(-1, 8))
assert SetExpr(Interval(-1, 1))**0 == SetExpr(FiniteSet(1))
#assert SetExpr(Interval(1, 2))**(S(5)/2) == SetExpr(Interval(1, 4*sqrt(2)))
#assert SetExpr(Interval(-1, 2))**(S.One/3) == SetExpr(Interval(-1, 2**(S.One/3)))
#assert SetExpr(Interval(0, 2))**(S.One/2) == SetExpr(Interval(0, sqrt(2)))
#assert SetExpr(Interval(-4, 2))**(S(2)/3) == SetExpr(Interval(0, 2*2**(S.One/3)))
#assert SetExpr(Interval(-1, 5))**(S.One/2) == SetExpr(Interval(0, sqrt(5)))
#assert SetExpr(Interval(-oo, 2))**(S.One/2) == SetExpr(Interval(0, sqrt(2)))
#assert SetExpr(Interval(-2, 3))**(S(-1)/4) == SetExpr(Interval(0, oo))
assert SetExpr(Interval(1, 5))**(-2) == SetExpr(Interval(S.One / 25, 1))
assert SetExpr(Interval(-1, 3))**(-2) == SetExpr(Interval(0, oo))
assert SetExpr(Interval(0, 2))**(-2) == SetExpr(Interval(S.One / 4, oo))
assert SetExpr(Interval(-1, 2))**(-3) == SetExpr(
Union(Interval(-oo, -1), Interval(S(1) / 8, oo)))
assert SetExpr(Interval(-3, -2))**(-3) == SetExpr(
Interval(S(-1) / 8, -S.One / 27))
assert SetExpr(Interval(-3, -2))**(-2) == SetExpr(
Interval(S.One / 9, S.One / 4))
#assert SetExpr(Interval(0, oo))**(S.One/2) == SetExpr(Interval(0, oo))
#assert SetExpr(Interval(-oo, -1))**(S.One/3) == SetExpr(Interval(-oo, -1))
#assert SetExpr(Interval(-2, 3))**(-S.One/3) == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-oo, 0))**(-2) == SetExpr(Interval.open(0, oo))
assert SetExpr(Interval(-2, 0))**(-2) == SetExpr(Interval(S.One / 4, oo))
assert SetExpr(Interval(S.One / 3, S.One / 2))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(0, S.One / 2))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(S.One / 2, 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(0, 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(2, 3))**oo == SetExpr(FiniteSet(oo))
assert SetExpr(Interval(1, 2))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(S.One / 2, 3))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(-S.One / 3,
-S.One / 4))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(-1, -S.One / 2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-3, -2))**oo == SetExpr(FiniteSet(-oo, oo))
assert SetExpr(Interval(-2, -1))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-2, -S.One / 2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-S.One / 2,
S.One / 2))**oo == SetExpr(FiniteSet(0))
assert SetExpr(Interval(-S.One / 2, 1))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(-S(2) / 3, 2))**oo == SetExpr(Interval(0, oo))
assert SetExpr(Interval(-1, 1))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-1, S.One / 2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-1, 2))**oo == SetExpr(Interval(-oo, oo))
assert SetExpr(Interval(-2, S.One / 2))**oo == SetExpr(Interval(-oo, oo))
assert (SetExpr(Interval(1, 2))**x).dummy_eq(
SetExpr(ImageSet(Lambda(_d, _d**x), Interval(1, 2))))
assert SetExpr(Interval(2, 3))**(-oo) == SetExpr(FiniteSet(0))
assert SetExpr(Interval(0, 2))**(-oo) == SetExpr(Interval(0, oo))
assert (SetExpr(Interval(-1, 2))**(-oo)).dummy_eq(
SetExpr(ImageSet(Lambda(_d, _d**(-oo)), Interval(-1, 2))))