Source code for diofant.polys.constructor

"""Tools for constructing domains for expressions. """

from ..core import I, sympify
from ..domains import EX, QQ, RR, ZZ
from ..domains.realfield import RealField
from .polyerrors import GeneratorsNeeded
from .polyoptions import build_options
from .polyutils import parallel_dict_from_basic


__all__ = 'construct_domain',


def _construct_simple(coeffs, opt):
    """Handle simple domains, e.g.: ZZ, QQ, RR and algebraic domains. """
    result, rationals, reals, algebraics = {}, False, False, False

    if opt.extension is False:
        def is_algebraic(coeff):
            return False
    else:
        def is_algebraic(coeff):
            return coeff.is_number and coeff.is_algebraic and not coeff.is_rational

    for coeff in coeffs:
        if coeff.is_Rational:
            if not coeff.is_Integer:
                rationals = True
        elif coeff.is_Float:
            if not algebraics:
                reals = True
            else:
                # there are both reals and algebraics -> EX
                return False
        elif is_algebraic(coeff):
            if not reals:
                algebraics = True
            else:
                # there are both algebraics and reals -> EX
                return False
        else:
            # this is a composite domain, e.g. ZZ[X], EX
            return

    if algebraics:
        domain, result = _construct_algebraic(coeffs, opt)
    else:
        if reals:
            # Use the maximum precision of all coefficients for the RR's
            # precision
            max_prec = max(c._prec for c in coeffs)
            domain = RealField(prec=max_prec)
        else:
            if opt.field or rationals:
                domain = QQ
            else:
                domain = ZZ

        result = []

        for coeff in coeffs:
            result.append(domain.convert(coeff))

    return domain, result


def _construct_algebraic(coeffs, opt):
    """We know that coefficients are algebraic so construct the extension. """

    result, exts = [], set()

    for coeff in coeffs:
        if coeff.is_Rational:
            coeff = (None, 0, QQ.convert(coeff))
        else:
            a = coeff.as_coeff_add()[0]
            coeff -= a

            b = coeff.as_coeff_mul()[0]
            coeff /= b

            exts.add(coeff)

            a = QQ.convert(a)
            b = QQ.convert(b)

            coeff = (coeff, b, a)

        result.append(coeff)

    exts = list(exts)

    if all(e.is_real for e in exts):
        domain = QQ.algebraic_field(*exts)
    else:
        ground_exts = list(set().union(*[_.as_real_imag() for _ in exts]))
        domain = QQ.algebraic_field(*ground_exts).algebraic_field(I)

    H = [domain.from_expr(e).rep for e in exts]

    for i, (coeff, a, b) in enumerate(result):
        if coeff is not None:
            coeff = a*domain.dtype(H[exts.index(coeff)]) + b
        else:
            coeff = domain.dtype([b])

        result[i] = coeff

    return domain, result


def _construct_composite(coeffs, opt):
    """Handle composite domains, e.g.: ZZ[X], QQ[X], ZZ(X), QQ(X). """
    numers, denoms = [], []

    for coeff in coeffs:
        numer, denom = coeff.as_numer_denom()

        numers.append(numer)
        denoms.append(denom)

    try:
        polys, gens = parallel_dict_from_basic(numers + denoms)  # XXX: sorting
    except GeneratorsNeeded:
        return

    if opt.composite is None:
        if any(g.is_number and not g.is_transcendental for g in gens):
            return  # generators are number-like so lets better use EX

        all_symbols = set()

        for gen in gens:
            symbols = gen.free_symbols

            if all_symbols & symbols:
                return  # there could be algebraic relations between generators
            else:
                all_symbols |= symbols

    n = len(gens)
    k = len(polys)//2

    numers = polys[:k]
    denoms = polys[k:]

    if opt.field:
        fractions = True
    else:
        fractions, zeros = False, (0,)*n

        for denom in denoms:
            if len(denom) > 1 or zeros not in denom:
                fractions = True
                break

    coeffs = set()

    if not fractions:
        for numer, denom in zip(numers, denoms):
            denom = denom[zeros]

            for monom, coeff in numer.items():
                coeff /= denom
                coeffs.add(coeff)
                numer[monom] = coeff
    else:
        for numer, denom in zip(numers, denoms):
            coeffs.update(list(numer.values()))
            coeffs.update(list(denom.values()))

    rationals, reals = False, False

    for coeff in coeffs:
        if coeff.is_Rational:
            if not coeff.is_Integer:
                rationals = True
        elif coeff.is_Float:
            reals = True
            break
        else:
            raise NotImplementedError

    if reals:
        ground = RR
    elif rationals:
        ground = QQ
    else:
        ground = ZZ

    result = []

    if not fractions:
        domain = ground.poly_ring(*gens)

        for numer in numers:
            for monom, coeff in numer.items():
                numer[monom] = ground.convert(coeff)

            result.append(domain(numer))
    else:
        domain = ground.frac_field(*gens)

        for numer, denom in zip(numers, denoms):
            for monom, coeff in numer.items():
                numer[monom] = ground.convert(coeff)

            for monom, coeff in denom.items():
                denom[monom] = ground.convert(coeff)

            result.append(domain((numer, denom)))

    return domain, result


def _construct_expression(coeffs, opt):
    """The last resort case, i.e. use the expression domain. """
    domain, result = EX, []

    for coeff in coeffs:
        result.append(domain.convert(coeff))

    return domain, result


[docs]def construct_domain(obj, **args): """Construct a minimal domain for the list of coefficients. """ opt = build_options(args) if hasattr(obj, '__iter__'): if isinstance(obj, dict): if not obj: monoms, coeffs = [], [] else: monoms, coeffs = list(zip(*list(obj.items()))) else: coeffs = obj else: coeffs = [obj] coeffs = list(map(sympify, coeffs)) result = _construct_simple(coeffs, opt) if result is not None: if result is not False: domain, coeffs = result else: domain, coeffs = _construct_expression(coeffs, opt) else: if opt.composite is False: result = None else: result = _construct_composite(coeffs, opt) if result is not None: domain, coeffs = result else: domain, coeffs = _construct_expression(coeffs, opt) if hasattr(obj, '__iter__'): if isinstance(obj, dict): return domain, dict(zip(monoms, coeffs)) else: return domain, coeffs else: return domain, coeffs[0]