395 lines
11 KiB
Python
395 lines
11 KiB
Python
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"""Computations with ideals of polynomial rings."""
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from sympy.polys.polyerrors import CoercionFailed
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from sympy.polys.polyutils import IntegerPowerable
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class Ideal(IntegerPowerable):
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"""
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Abstract base class for ideals.
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Do not instantiate - use explicit constructors in the ring class instead:
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>>> from sympy import QQ
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>>> from sympy.abc import x
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>>> QQ.old_poly_ring(x).ideal(x+1)
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<x + 1>
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Attributes
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- ring - the ring this ideal belongs to
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Non-implemented methods:
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- _contains_elem
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- _contains_ideal
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- _quotient
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- _intersect
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- _union
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- _product
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- is_whole_ring
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- is_zero
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- is_prime, is_maximal, is_primary, is_radical
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- is_principal
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- height, depth
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- radical
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Methods that likely should be overridden in subclasses:
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- reduce_element
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"""
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def _contains_elem(self, x):
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"""Implementation of element containment."""
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raise NotImplementedError
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def _contains_ideal(self, I):
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"""Implementation of ideal containment."""
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raise NotImplementedError
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def _quotient(self, J):
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"""Implementation of ideal quotient."""
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raise NotImplementedError
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def _intersect(self, J):
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"""Implementation of ideal intersection."""
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raise NotImplementedError
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def is_whole_ring(self):
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"""Return True if ``self`` is the whole ring."""
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raise NotImplementedError
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def is_zero(self):
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"""Return True if ``self`` is the zero ideal."""
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raise NotImplementedError
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def _equals(self, J):
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"""Implementation of ideal equality."""
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return self._contains_ideal(J) and J._contains_ideal(self)
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def is_prime(self):
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"""Return True if ``self`` is a prime ideal."""
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raise NotImplementedError
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def is_maximal(self):
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"""Return True if ``self`` is a maximal ideal."""
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raise NotImplementedError
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def is_radical(self):
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"""Return True if ``self`` is a radical ideal."""
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raise NotImplementedError
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def is_primary(self):
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"""Return True if ``self`` is a primary ideal."""
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raise NotImplementedError
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def is_principal(self):
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"""Return True if ``self`` is a principal ideal."""
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raise NotImplementedError
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def radical(self):
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"""Compute the radical of ``self``."""
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raise NotImplementedError
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def depth(self):
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"""Compute the depth of ``self``."""
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raise NotImplementedError
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def height(self):
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"""Compute the height of ``self``."""
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raise NotImplementedError
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# TODO more
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# non-implemented methods end here
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def __init__(self, ring):
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self.ring = ring
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def _check_ideal(self, J):
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"""Helper to check ``J`` is an ideal of our ring."""
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if not isinstance(J, Ideal) or J.ring != self.ring:
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raise ValueError(
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'J must be an ideal of %s, got %s' % (self.ring, J))
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def contains(self, elem):
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"""
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Return True if ``elem`` is an element of this ideal.
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Examples
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========
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>>> from sympy.abc import x
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>>> from sympy import QQ
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>>> QQ.old_poly_ring(x).ideal(x+1, x-1).contains(3)
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True
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>>> QQ.old_poly_ring(x).ideal(x**2, x**3).contains(x)
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False
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"""
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return self._contains_elem(self.ring.convert(elem))
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def subset(self, other):
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"""
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Returns True if ``other`` is is a subset of ``self``.
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Here ``other`` may be an ideal.
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Examples
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========
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>>> from sympy.abc import x
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>>> from sympy import QQ
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>>> I = QQ.old_poly_ring(x).ideal(x+1)
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>>> I.subset([x**2 - 1, x**2 + 2*x + 1])
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True
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>>> I.subset([x**2 + 1, x + 1])
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False
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>>> I.subset(QQ.old_poly_ring(x).ideal(x**2 - 1))
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True
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"""
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if isinstance(other, Ideal):
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return self._contains_ideal(other)
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return all(self._contains_elem(x) for x in other)
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def quotient(self, J, **opts):
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r"""
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Compute the ideal quotient of ``self`` by ``J``.
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That is, if ``self`` is the ideal `I`, compute the set
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`I : J = \{x \in R | xJ \subset I \}`.
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Examples
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========
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>>> from sympy.abc import x, y
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>>> from sympy import QQ
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>>> R = QQ.old_poly_ring(x, y)
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>>> R.ideal(x*y).quotient(R.ideal(x))
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<y>
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"""
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self._check_ideal(J)
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return self._quotient(J, **opts)
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def intersect(self, J):
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"""
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Compute the intersection of self with ideal J.
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Examples
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========
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>>> from sympy.abc import x, y
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>>> from sympy import QQ
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>>> R = QQ.old_poly_ring(x, y)
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>>> R.ideal(x).intersect(R.ideal(y))
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<x*y>
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"""
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self._check_ideal(J)
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return self._intersect(J)
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def saturate(self, J):
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r"""
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Compute the ideal saturation of ``self`` by ``J``.
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That is, if ``self`` is the ideal `I`, compute the set
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`I : J^\infty = \{x \in R | xJ^n \subset I \text{ for some } n\}`.
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"""
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raise NotImplementedError
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# Note this can be implemented using repeated quotient
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def union(self, J):
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"""
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Compute the ideal generated by the union of ``self`` and ``J``.
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Examples
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========
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>>> from sympy.abc import x
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>>> from sympy import QQ
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>>> QQ.old_poly_ring(x).ideal(x**2 - 1).union(QQ.old_poly_ring(x).ideal((x+1)**2)) == QQ.old_poly_ring(x).ideal(x+1)
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True
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"""
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self._check_ideal(J)
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return self._union(J)
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def product(self, J):
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r"""
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Compute the ideal product of ``self`` and ``J``.
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That is, compute the ideal generated by products `xy`, for `x` an element
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of ``self`` and `y \in J`.
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Examples
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========
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>>> from sympy.abc import x, y
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>>> from sympy import QQ
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>>> QQ.old_poly_ring(x, y).ideal(x).product(QQ.old_poly_ring(x, y).ideal(y))
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<x*y>
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"""
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self._check_ideal(J)
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return self._product(J)
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def reduce_element(self, x):
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"""
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Reduce the element ``x`` of our ring modulo the ideal ``self``.
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Here "reduce" has no specific meaning: it could return a unique normal
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form, simplify the expression a bit, or just do nothing.
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"""
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return x
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def __add__(self, e):
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if not isinstance(e, Ideal):
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R = self.ring.quotient_ring(self)
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if isinstance(e, R.dtype):
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return e
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if isinstance(e, R.ring.dtype):
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return R(e)
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return R.convert(e)
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self._check_ideal(e)
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return self.union(e)
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__radd__ = __add__
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def __mul__(self, e):
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if not isinstance(e, Ideal):
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try:
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e = self.ring.ideal(e)
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except CoercionFailed:
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return NotImplemented
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self._check_ideal(e)
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return self.product(e)
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__rmul__ = __mul__
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def _zeroth_power(self):
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return self.ring.ideal(1)
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def _first_power(self):
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# Raising to any power but 1 returns a new instance. So we mult by 1
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# here so that the first power is no exception.
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return self * 1
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def __eq__(self, e):
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if not isinstance(e, Ideal) or e.ring != self.ring:
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return False
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return self._equals(e)
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def __ne__(self, e):
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return not (self == e)
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class ModuleImplementedIdeal(Ideal):
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"""
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Ideal implementation relying on the modules code.
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Attributes:
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- _module - the underlying module
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"""
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def __init__(self, ring, module):
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Ideal.__init__(self, ring)
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self._module = module
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def _contains_elem(self, x):
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return self._module.contains([x])
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def _contains_ideal(self, J):
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if not isinstance(J, ModuleImplementedIdeal):
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raise NotImplementedError
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return self._module.is_submodule(J._module)
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def _intersect(self, J):
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if not isinstance(J, ModuleImplementedIdeal):
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raise NotImplementedError
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return self.__class__(self.ring, self._module.intersect(J._module))
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def _quotient(self, J, **opts):
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if not isinstance(J, ModuleImplementedIdeal):
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raise NotImplementedError
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return self._module.module_quotient(J._module, **opts)
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def _union(self, J):
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if not isinstance(J, ModuleImplementedIdeal):
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raise NotImplementedError
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return self.__class__(self.ring, self._module.union(J._module))
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@property
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def gens(self):
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"""
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Return generators for ``self``.
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Examples
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========
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>>> from sympy import QQ
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>>> from sympy.abc import x, y
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>>> list(QQ.old_poly_ring(x, y).ideal(x, y, x**2 + y).gens)
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[x, y, x**2 + y]
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"""
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return (x[0] for x in self._module.gens)
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def is_zero(self):
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"""
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Return True if ``self`` is the zero ideal.
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Examples
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========
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>>> from sympy.abc import x
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>>> from sympy import QQ
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>>> QQ.old_poly_ring(x).ideal(x).is_zero()
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False
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>>> QQ.old_poly_ring(x).ideal().is_zero()
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True
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"""
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return self._module.is_zero()
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def is_whole_ring(self):
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"""
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Return True if ``self`` is the whole ring, i.e. one generator is a unit.
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Examples
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========
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>>> from sympy.abc import x
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>>> from sympy import QQ, ilex
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>>> QQ.old_poly_ring(x).ideal(x).is_whole_ring()
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False
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>>> QQ.old_poly_ring(x).ideal(3).is_whole_ring()
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True
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>>> QQ.old_poly_ring(x, order=ilex).ideal(2 + x).is_whole_ring()
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True
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"""
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return self._module.is_full_module()
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def __repr__(self):
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from sympy.printing.str import sstr
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return '<' + ','.join(sstr(x) for [x] in self._module.gens) + '>'
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# NOTE this is the only method using the fact that the module is a SubModule
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def _product(self, J):
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if not isinstance(J, ModuleImplementedIdeal):
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raise NotImplementedError
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return self.__class__(self.ring, self._module.submodule(
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*[[x*y] for [x] in self._module.gens for [y] in J._module.gens]))
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def in_terms_of_generators(self, e):
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"""
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Express ``e`` in terms of the generators of ``self``.
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Examples
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========
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>>> from sympy.abc import x
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>>> from sympy import QQ
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>>> I = QQ.old_poly_ring(x).ideal(x**2 + 1, x)
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>>> I.in_terms_of_generators(1)
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[1, -x]
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"""
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return self._module.in_terms_of_generators([e])
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def reduce_element(self, x, **options):
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return self._module.reduce_element([x], **options)[0]
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