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from __future__ import print_function, division
from sympy.core import S, sympify from sympy.core.add import Add from sympy.core.containers import Tuple from sympy.core.operations import LatticeOp, ShortCircuit from sympy.core.function import Application, Lambda, ArgumentIndexError from sympy.core.expr import Expr from sympy.core.mul import Mul from sympy.core.numbers import Rational from sympy.core.power import Pow from sympy.core.relational import Equality from sympy.core.singleton import Singleton from sympy.core.symbol import Dummy from sympy.core.rules import Transform from sympy.core.compatibility import as_int, with_metaclass, range from sympy.core.logic import fuzzy_and, fuzzy_or, _torf from sympy.functions.elementary.integers import floor from sympy.logic.boolalg import And
class IdentityFunction(with_metaclass(Singleton, Lambda)): """ The identity function
Examples ========
>>> from sympy import Id, Symbol >>> x = Symbol('x') >>> Id(x) x
"""
def __new__(cls): from sympy.sets.sets import FiniteSet x = Dummy('x') #construct "by hand" to avoid infinite loop obj = Expr.__new__(cls, Tuple(x), x) obj.nargs = FiniteSet(1) return obj
Id = S.IdentityFunction
############################################################################### ############################# ROOT and SQUARE ROOT FUNCTION ################### ###############################################################################
def sqrt(arg): """The square root function
sqrt(x) -> Returns the principal square root of x.
Examples ========
>>> from sympy import sqrt, Symbol >>> x = Symbol('x')
>>> sqrt(x) sqrt(x)
>>> sqrt(x)**2 x
Note that sqrt(x**2) does not simplify to x.
>>> sqrt(x**2) sqrt(x**2)
This is because the two are not equal to each other in general. For example, consider x == -1:
>>> from sympy import Eq >>> Eq(sqrt(x**2), x).subs(x, -1) False
This is because sqrt computes the principal square root, so the square may put the argument in a different branch. This identity does hold if x is positive:
>>> y = Symbol('y', positive=True) >>> sqrt(y**2) y
You can force this simplification by using the powdenest() function with the force option set to True:
>>> from sympy import powdenest >>> sqrt(x**2) sqrt(x**2) >>> powdenest(sqrt(x**2), force=True) x
To get both branches of the square root you can use the rootof function:
>>> from sympy import rootof
>>> [rootof(x**2-3,i) for i in (0,1)] [-sqrt(3), sqrt(3)]
See Also ========
sympy.polys.rootoftools.rootof, root, real_root
References ==========
.. [1] http://en.wikipedia.org/wiki/Square_root .. [2] http://en.wikipedia.org/wiki/Principal_value """ # arg = sympify(arg) is handled by Pow
def cbrt(arg): """This function computes the principial cube root of `arg`, so it's just a shortcut for `arg**Rational(1, 3)`.
Examples ========
>>> from sympy import cbrt, Symbol >>> x = Symbol('x')
>>> cbrt(x) x**(1/3)
>>> cbrt(x)**3 x
Note that cbrt(x**3) does not simplify to x.
>>> cbrt(x**3) (x**3)**(1/3)
This is because the two are not equal to each other in general. For example, consider `x == -1`:
>>> from sympy import Eq >>> Eq(cbrt(x**3), x).subs(x, -1) False
This is because cbrt computes the principal cube root, this identity does hold if `x` is positive:
>>> y = Symbol('y', positive=True) >>> cbrt(y**3) y
See Also ========
sympy.polys.rootoftools.rootof, root, real_root
References ==========
* http://en.wikipedia.org/wiki/Cube_root * http://en.wikipedia.org/wiki/Principal_value
""" return Pow(arg, Rational(1, 3))
def root(arg, n, k=0): """root(x, n, k) -> Returns the k-th n-th root of x, defaulting to the principle root (k=0).
Examples ========
>>> from sympy import root, Rational >>> from sympy.abc import x, n
>>> root(x, 2) sqrt(x)
>>> root(x, 3) x**(1/3)
>>> root(x, n) x**(1/n)
>>> root(x, -Rational(2, 3)) x**(-3/2)
To get the k-th n-th root, specify k:
>>> root(-2, 3, 2) -(-1)**(2/3)*2**(1/3)
To get all n n-th roots you can use the rootof function. The following examples show the roots of unity for n equal 2, 3 and 4:
>>> from sympy import rootof, I
>>> [rootof(x**2 - 1, i) for i in range(2)] [-1, 1]
>>> [rootof(x**3 - 1,i) for i in range(3)] [1, -1/2 - sqrt(3)*I/2, -1/2 + sqrt(3)*I/2]
>>> [rootof(x**4 - 1,i) for i in range(4)] [-1, 1, -I, I]
SymPy, like other symbolic algebra systems, returns the complex root of negative numbers. This is the principal root and differs from the text-book result that one might be expecting. For example, the cube root of -8 does not come back as -2:
>>> root(-8, 3) 2*(-1)**(1/3)
The real_root function can be used to either make the principle result real (or simply to return the real root directly):
>>> from sympy import real_root >>> real_root(_) -2 >>> real_root(-32, 5) -2
Alternatively, the n//2-th n-th root of a negative number can be computed with root:
>>> root(-32, 5, 5//2) -2
See Also ========
sympy.polys.rootoftools.rootof sympy.core.power.integer_nthroot sqrt, real_root
References ==========
* http://en.wikipedia.org/wiki/Square_root * http://en.wikipedia.org/wiki/Real_root * http://en.wikipedia.org/wiki/Root_of_unity * http://en.wikipedia.org/wiki/Principal_value * http://mathworld.wolfram.com/CubeRoot.html
""" return Pow(arg, S.One/n)*S.NegativeOne**(2*k/n)
def real_root(arg, n=None): """Return the real nth-root of arg if possible. If n is omitted then all instances of (-n)**(1/odd) will be changed to -n**(1/odd); this will only create a real root of a principle root -- the presence of other factors may cause the result to not be real.
Examples ========
>>> from sympy import root, real_root, Rational >>> from sympy.abc import x, n
>>> real_root(-8, 3) -2 >>> root(-8, 3) 2*(-1)**(1/3) >>> real_root(_) -2
If one creates a non-principle root and applies real_root, the result will not be real (so use with caution):
>>> root(-8, 3, 2) -2*(-1)**(2/3) >>> real_root(_) -2*(-1)**(2/3)
See Also ========
sympy.polys.rootoftools.rootof sympy.core.power.integer_nthroot root, sqrt """ rv = root(arg, n) else: (S.One, ~Equality(im(arg), 0)), (Pow(S.NegativeOne, S.One/n)**(2*floor(n/2)), And( Equality(n % 2, 1), arg < 0)), (S.One, True)) else: rv = sympify(arg) n1pow = Transform(lambda x: -(-x.base)**x.exp, lambda x: x.is_Pow and x.base.is_negative and x.exp.is_Rational and x.exp.p == 1 and x.exp.q % 2) return rv.xreplace(n1pow)
############################################################################### ############################# MINIMUM and MAXIMUM ############################# ###############################################################################
class MinMaxBase(Expr, LatticeOp): def __new__(cls, *args, **assumptions):
# first standard filter, for cls.zero and cls.identity # also reshape Max(a, Max(b, c)) to Max(a, b, c)
# second filter # variant I: remove ones which can be removed # args = cls._collapse_arguments(set(_args), **assumptions)
# variant II: find local zeros
else: # base creation # XXX should _args be made canonical with sorting?
@classmethod def _new_args_filter(cls, arg_sequence): """ Generator filtering args.
first standard filter, for cls.zero and cls.identity. Also reshape Max(a, Max(b, c)) to Max(a, b, c), and check arguments for comparability """
# pre-filter, checking comparability of arguments
for x in arg.args: yield x else:
@classmethod def _find_localzeros(cls, values, **options): """ Sequentially allocate values to localzeros.
When a value is identified as being more extreme than another member it replaces that member; if this is never true, then the value is simply appended to the localzeros. """ is_newzero = False else:
@classmethod def _is_connected(cls, x, y): """ Check if x and y are connected somehow. """ return True return r return r # simplification can be expensive, so be conservative # in what is attempted
def _eval_derivative(self, s): # f(x).diff(s) -> x.diff(s) * f.fdiff(1)(s) i = 0 l = [] for a in self.args: i += 1 da = a.diff(s) if da is S.Zero: continue try: df = self.fdiff(i) except ArgumentIndexError: df = Function.fdiff(self, i) l.append(df * da) return Add(*l)
def evalf(self, prec=None, **options): return self.func(*[a.evalf(prec, **options) for a in self.args]) n = evalf
_eval_is_commutative = lambda s: _torf(i.is_commutative for i in s.args) _eval_is_negative = lambda s: _torf(i.is_negative for i in s.args) _eval_is_nonnegative = lambda s: _torf(i.is_nonnegative for i in s.args) _eval_is_polar = lambda s: _torf(i.is_polar for i in s.args) _eval_is_positive = lambda s: _torf(i.is_positive for i in s.args)
class Max(MinMaxBase, Application): """ Return, if possible, the maximum value of the list.
When number of arguments is equal one, then return this argument.
When number of arguments is equal two, then return, if possible, the value from (a, b) that is >= the other.
In common case, when the length of list greater than 2, the task is more complicated. Return only the arguments, which are greater than others, if it is possible to determine directional relation.
If is not possible to determine such a relation, return a partially evaluated result.
Assumptions are used to make the decision too.
Also, only comparable arguments are permitted.
It is named ``Max`` and not ``max`` to avoid conflicts with the built-in function ``max``.
Examples ========
>>> from sympy import Max, Symbol, oo >>> from sympy.abc import x, y >>> p = Symbol('p', positive=True) >>> n = Symbol('n', negative=True)
>>> Max(x, -2) #doctest: +SKIP Max(x, -2) >>> Max(x, -2).subs(x, 3) 3 >>> Max(p, -2) p >>> Max(x, y) #doctest: +SKIP Max(x, y) >>> Max(x, y) == Max(y, x) True >>> Max(x, Max(y, z)) #doctest: +SKIP Max(x, y, z) >>> Max(n, 8, p, 7, -oo) #doctest: +SKIP Max(8, p) >>> Max (1, x, oo) oo
* Algorithm
The task can be considered as searching of supremums in the directed complete partial orders [1]_.
The source values are sequentially allocated by the isolated subsets in which supremums are searched and result as Max arguments.
If the resulted supremum is single, then it is returned.
The isolated subsets are the sets of values which are only the comparable with each other in the current set. E.g. natural numbers are comparable with each other, but not comparable with the `x` symbol. Another example: the symbol `x` with negative assumption is comparable with a natural number.
Also there are "least" elements, which are comparable with all others, and have a zero property (maximum or minimum for all elements). E.g. `oo`. In case of it the allocation operation is terminated and only this value is returned.
Assumption: - if A > B > C then A > C - if A == B then B can be removed
References ==========
.. [1] http://en.wikipedia.org/wiki/Directed_complete_partial_order .. [2] http://en.wikipedia.org/wiki/Lattice_%28order%29
See Also ========
Min : find minimum values """ zero = S.Infinity identity = S.NegativeInfinity
def fdiff( self, argindex ): from sympy import Heaviside n = len(self.args) if 0 < argindex and argindex <= n: argindex -= 1 if n == 2: return Heaviside(self.args[argindex] - self.args[1 - argindex]) newargs = tuple([self.args[i] for i in range(n) if i != argindex]) return Heaviside(self.args[argindex] - Max(*newargs)) else: raise ArgumentIndexError(self, argindex)
def _eval_rewrite_as_Heaviside(self, *args): from sympy import Heaviside return Add(*[j*Mul(*[Heaviside(j - i) for i in args if i!=j]) \ for j in args])
def _eval_is_positive(self): return fuzzy_or(a.is_positive for a in self.args)
def _eval_is_nonnegative(self): return fuzzy_or(a.is_nonnegative for a in self.args)
def _eval_is_negative(self): return fuzzy_and(a.is_negative for a in self.args)
class Min(MinMaxBase, Application): """ Return, if possible, the minimum value of the list. It is named ``Min`` and not ``min`` to avoid conflicts with the built-in function ``min``.
Examples ========
>>> from sympy import Min, Symbol, oo >>> from sympy.abc import x, y >>> p = Symbol('p', positive=True) >>> n = Symbol('n', negative=True)
>>> Min(x, -2) #doctest: +SKIP Min(x, -2) >>> Min(x, -2).subs(x, 3) -2 >>> Min(p, -3) -3 >>> Min(x, y) #doctest: +SKIP Min(x, y) >>> Min(n, 8, p, -7, p, oo) #doctest: +SKIP Min(n, -7)
See Also ========
Max : find maximum values """ zero = S.NegativeInfinity identity = S.Infinity
def fdiff( self, argindex ): from sympy import Heaviside n = len(self.args) if 0 < argindex and argindex <= n: argindex -= 1 if n == 2: return Heaviside( self.args[1-argindex] - self.args[argindex] ) newargs = tuple([ self.args[i] for i in range(n) if i != argindex]) return Heaviside( Min(*newargs) - self.args[argindex] ) else: raise ArgumentIndexError(self, argindex)
def _eval_rewrite_as_Heaviside(self, *args): from sympy import Heaviside return Add(*[j*Mul(*[Heaviside(i-j) for i in args if i!=j]) \ for j in args])
def _eval_is_positive(self):
def _eval_is_nonnegative(self):
def _eval_is_negative(self): |