def solveset_real(f, symbol):
""" Solves a real valued equation.
Parameters
==========
f : Expr
The target equation
symbol : Symbol
The variable for which the equation is solved
Returns
=======
Set
A set of values for `symbol` for which `f` is equal to
zero. An `EmptySet` is returned if no solution is found.
A `ConditionSet` is returned as unsolved object if algorithms
to evaluate complete solutions are not yet implemented.
`solveset_real` claims to be complete in the set of the solution it
returns.
Raises
======
NotImplementedError
Algorithms to solve inequalities in complex domain are
not yet implemented.
ValueError
The input is not valid.
RuntimeError
It is a bug, please report to the github issue tracker.
See Also
=======
solveset_complex : solver for complex domain
Examples
========
>>> from sympy import Symbol, exp, sin, sqrt, I
>>> from sympy.solvers.solveset import solveset_real
>>> x = Symbol('x', real=True)
>>> a = Symbol('a', real=True, finite=True, positive=True)
>>> solveset_real(x**2 - 1, x)
{-1, 1}
>>> solveset_real(sqrt(5*x + 6) - 2 - x, x)
{-1, 2}
>>> solveset_real(x - I, x)
EmptySet()
>>> solveset_real(x - a, x)
{a}
>>> solveset_real(exp(x) - a, x)
{log(a)}
* In case the equation has infinitely many solutions an infinitely indexed
`ImageSet` is returned.
>>> solveset_real(sin(x) - 1, x)
ImageSet(Lambda(_n, 2*_n*pi + pi/2), Integers())
* If the equation is true for any arbitrary value of the symbol a `S.Reals`
set is returned.
>>> solveset_real(x - x, x)
(-oo, oo)
"""
if not symbol.is_Symbol:
raise ValueError(" %s is not a symbol" % (symbol))
f = sympify(f)
if not isinstance(f, (Expr, Number)):
raise ValueError(" %s is not a valid sympy expression" % (f))
original_eq = f
f = together(f)
# In this, unlike in solveset_complex, expression should only
# be expanded when fraction(f)[1] does not contain the symbol
# for which we are solving
if not symbol in fraction(f)[1].free_symbols and f.is_rational_function():
f = expand(f)
if f.has(Piecewise):
f = piecewise_fold(f)
result = EmptySet()
if f.expand().is_zero:
return S.Reals
elif not f.has(symbol):
return EmptySet()
elif f.is_Mul and all([_is_finite_with_finite_vars(m) for m in f.args]):
# if f(x) and g(x) are both finite we can say that the solution of
# f(x)*g(x) == 0 is same as Union(f(x) == 0, g(x) == 0) is not true in
# general. g(x) can grow to infinitely large for the values where
# f(x) == 0. To be sure that we are not silently allowing any
# wrong solutions we are using this technique only if both f and g are
# finite for a finite input.
result = Union(*[solveset_real(m, symbol) for m in f.args])
elif _is_function_class_equation(TrigonometricFunction, f, symbol) or \
_is_function_class_equation(HyperbolicFunction, f, symbol):
result = _solve_real_trig(f, symbol)
elif f.is_Piecewise:
result = EmptySet()
expr_set_pairs = f.as_expr_set_pairs()
for (expr, in_set) in expr_set_pairs:
solns = solveset_real(expr, symbol).intersect(in_set)
result = result + solns
else:
lhs, rhs_s = invert_real(f, 0, symbol)
if lhs == symbol:
result = rhs_s
elif isinstance(rhs_s, FiniteSet):
equations = [lhs - rhs for rhs in rhs_s]
for equation in equations:
if equation == f:
if any(
_has_rational_power(g, symbol)[0]
for g in equation.args):
result += _solve_radical(equation, symbol,
solveset_real)
elif equation.has(Abs):
result += _solve_abs(f, symbol)
else:
result += _solve_as_rational(
equation,
symbol,
solveset_solver=solveset_real,
as_poly_solver=_solve_as_poly_real)
else:
result += solveset_real(equation, symbol)
else:
result = ConditionSet(symbol, Eq(f, 0), S.Reals)
if isinstance(result, FiniteSet):
result = [
s for s in result
if isinstance(s, RootOf) or domain_check(original_eq, symbol, s)
]
return FiniteSet(*result).intersect(S.Reals)
else:
return result.intersect(S.Reals)
def solveset_real(f, symbol):
""" Solves a real valued equation.
Parameters
==========
f : Expr
The target equation
symbol : Symbol
The variable for which the equation is solved
Returns
=======
Set
A set of values for `symbol` for which `f` is equal to
zero. An `EmptySet` is returned if no solution is found.
`solveset_real` claims to be complete in the set of the solution it
returns.
Raises
======
NotImplementedError
The algorithms for to find the solution of the given equation are
not yet implemented.
ValueError
The input is not valid.
RuntimeError
It is a bug, please report to the github issue tracker.
See Also
=======
solveset_complex : solver for complex domain
Examples
========
>>> from sympy import Symbol, exp, sin, sqrt, I
>>> from sympy.solvers.solveset import solveset_real
>>> x = Symbol('x', real=True)
>>> a = Symbol('a', real=True, finite=True, positive=True)
>>> solveset_real(x**2 - 1, x)
{-1, 1}
>>> solveset_real(sqrt(5*x + 6) - 2 - x, x)
{-1, 2}
>>> solveset_real(x - I, x)
EmptySet()
>>> solveset_real(x - a, x)
{a}
>>> solveset_real(exp(x) - a, x)
{log(a)}
In case the equation has infinitely many solutions an infinitely indexed
`ImageSet` is returned.
>>> solveset_real(sin(x) - 1, x)
ImageSet(Lambda(_n, 2*_n*pi + pi/2), Integers())
If the equation is true for any arbitrary value of the symbol a `S.Reals`
set is returned.
>>> solveset_real(x - x, x)
(-oo, oo)
"""
if not symbol.is_Symbol:
raise ValueError(" %s is not a symbol" % (symbol))
f = sympify(f)
if not isinstance(f, (Expr, Number)):
raise ValueError(" %s is not a valid sympy expression" % (f))
original_eq = f
f = together(f)
if f.has(Piecewise):
f = piecewise_fold(f)
result = EmptySet()
if f.expand().is_zero:
return S.Reals
elif not f.has(symbol):
return EmptySet()
elif f.is_Mul and all([_is_finite_with_finite_vars(m) for m in f.args]):
# if f(x) and g(x) are both finite we can say that the solution of
# f(x)*g(x) == 0 is same as Union(f(x) == 0, g(x) == 0) is not true in
# general. g(x) can grow to infinitely large for the values where
# f(x) == 0. To be sure that we not are silently allowing any
# wrong solutions we are using this technique only if both f and g and
# finite for a finite input.
result = Union(*[solveset_real(m, symbol) for m in f.args])
elif _is_function_class_equation(C.TrigonometricFunction, f, symbol) or \
_is_function_class_equation(C.HyperbolicFunction, f, symbol):
result = _solve_real_trig(f, symbol)
elif f.is_Piecewise:
result = EmptySet()
expr_set_pairs = f.as_expr_set_pairs()
for (expr, in_set) in expr_set_pairs:
solns = solveset_real(expr, symbol).intersect(in_set)
result = result + solns
else:
lhs, rhs_s = invert_real(f, 0, symbol)
if lhs == symbol:
result = rhs_s
elif isinstance(rhs_s, FiniteSet):
equations = [lhs - rhs for rhs in rhs_s]
for equation in equations:
if equation == f:
if any(_has_rational_power(g, symbol)[0]
for g in equation.args):
result += _solve_radical(equation,
symbol,
solveset_real)
elif equation.has(Abs):
result += _solve_abs(f, symbol)
else:
result += _solve_as_rational(equation, symbol,
solveset_solver=solveset_real,
as_poly_solver=_solve_as_poly_real)
else:
result += solveset_real(equation, symbol)
else:
raise NotImplementedError
if isinstance(result, FiniteSet):
result = [s for s in result
if isinstance(s, RootOf)
or domain_check(original_eq, symbol, s)]
return FiniteSet(*result).intersect(S.Reals)
else:
return result.intersect(S.Reals)
