switching to high quality piper tts and added label translations

2026-01-29 23:48:19 +01:00
commit d80c619df9
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+from sympy.core import S
+from sympy.polys import Poly
+
+
+def dispersionset(p, q=None, *gens, **args):
+    r"""Compute the *dispersion set* of two polynomials.
+
+    For two polynomials `f(x)` and `g(x)` with `\deg f > 0`
+    and `\deg g > 0` the dispersion set `\operatorname{J}(f, g)` is defined as:
+
+    .. math::
+        \operatorname{J}(f, g)
+        & := \{a \in \mathbb{N}_0 | \gcd(f(x), g(x+a)) \neq 1\} \\
+        &  = \{a \in \mathbb{N}_0 | \deg \gcd(f(x), g(x+a)) \geq 1\}
+
+    For a single polynomial one defines `\operatorname{J}(f) := \operatorname{J}(f, f)`.
+
+    Examples
+    ========
+
+    >>> from sympy import poly
+    >>> from sympy.polys.dispersion import dispersion, dispersionset
+    >>> from sympy.abc import x
+
+    Dispersion set and dispersion of a simple polynomial:
+
+    >>> fp = poly((x - 3)*(x + 3), x)
+    >>> sorted(dispersionset(fp))
+    [0, 6]
+    >>> dispersion(fp)
+    6
+
+    Note that the definition of the dispersion is not symmetric:
+
+    >>> fp = poly(x**4 - 3*x**2 + 1, x)
+    >>> gp = fp.shift(-3)
+    >>> sorted(dispersionset(fp, gp))
+    [2, 3, 4]
+    >>> dispersion(fp, gp)
+    4
+    >>> sorted(dispersionset(gp, fp))
+    []
+    >>> dispersion(gp, fp)
+    -oo
+
+    Computing the dispersion also works over field extensions:
+
+    >>> from sympy import sqrt
+    >>> fp = poly(x**2 + sqrt(5)*x - 1, x, domain='QQ<sqrt(5)>')
+    >>> gp = poly(x**2 + (2 + sqrt(5))*x + sqrt(5), x, domain='QQ<sqrt(5)>')
+    >>> sorted(dispersionset(fp, gp))
+    [2]
+    >>> sorted(dispersionset(gp, fp))
+    [1, 4]
+
+    We can even perform the computations for polynomials
+    having symbolic coefficients:
+
+    >>> from sympy.abc import a
+    >>> fp = poly(4*x**4 + (4*a + 8)*x**3 + (a**2 + 6*a + 4)*x**2 + (a**2 + 2*a)*x, x)
+    >>> sorted(dispersionset(fp))
+    [0, 1]
+
+    See Also
+    ========
+
+    dispersion
+
+    References
+    ==========
+
+    .. [1] [ManWright94]_
+    .. [2] [Koepf98]_
+    .. [3] [Abramov71]_
+    .. [4] [Man93]_
+    """
+    # Check for valid input
+    same = False if q is not None else True
+    if same:
+        q = p
+
+    p = Poly(p, *gens, **args)
+    q = Poly(q, *gens, **args)
+
+    if not p.is_univariate or not q.is_univariate:
+        raise ValueError("Polynomials need to be univariate")
+
+    # The generator
+    if not p.gen == q.gen:
+        raise ValueError("Polynomials must have the same generator")
+    gen = p.gen
+
+    # We define the dispersion of constant polynomials to be zero
+    if p.degree() < 1 or q.degree() < 1:
+        return {0}
+
+    # Factor p and q over the rationals
+    fp = p.factor_list()
+    fq = q.factor_list() if not same else fp
+
+    # Iterate over all pairs of factors
+    J = set()
+    for s, unused in fp[1]:
+        for t, unused in fq[1]:
+            m = s.degree()
+            n = t.degree()
+            if n != m:
+                continue
+            an = s.LC()
+            bn = t.LC()
+            if not (an - bn).is_zero:
+                continue
+            # Note that the roles of `s` and `t` below are switched
+            # w.r.t. the original paper. This is for consistency
+            # with the description in the book of W. Koepf.
+            anm1 = s.coeff_monomial(gen**(m-1))
+            bnm1 = t.coeff_monomial(gen**(n-1))
+            alpha = (anm1 - bnm1) / S(n*bn)
+            if not alpha.is_integer:
+                continue
+            if alpha < 0 or alpha in J:
+                continue
+            if n > 1 and not (s - t.shift(alpha)).is_zero:
+                continue
+            J.add(alpha)
+
+    return J
+
+
+def dispersion(p, q=None, *gens, **args):
+    r"""Compute the *dispersion* of polynomials.
+
+    For two polynomials `f(x)` and `g(x)` with `\deg f > 0`
+    and `\deg g > 0` the dispersion `\operatorname{dis}(f, g)` is defined as:
+
+    .. math::
+        \operatorname{dis}(f, g)
+        & := \max\{ J(f,g) \cup \{0\} \} \\
+        &  = \max\{ \{a \in \mathbb{N} | \gcd(f(x), g(x+a)) \neq 1\} \cup \{0\} \}
+
+    and for a single polynomial `\operatorname{dis}(f) := \operatorname{dis}(f, f)`.
+    Note that we make the definition `\max\{\} := -\infty`.
+
+    Examples
+    ========
+
+    >>> from sympy import poly
+    >>> from sympy.polys.dispersion import dispersion, dispersionset
+    >>> from sympy.abc import x
+
+    Dispersion set and dispersion of a simple polynomial:
+
+    >>> fp = poly((x - 3)*(x + 3), x)
+    >>> sorted(dispersionset(fp))
+    [0, 6]
+    >>> dispersion(fp)
+    6
+
+    Note that the definition of the dispersion is not symmetric:
+
+    >>> fp = poly(x**4 - 3*x**2 + 1, x)
+    >>> gp = fp.shift(-3)
+    >>> sorted(dispersionset(fp, gp))
+    [2, 3, 4]
+    >>> dispersion(fp, gp)
+    4
+    >>> sorted(dispersionset(gp, fp))
+    []
+    >>> dispersion(gp, fp)
+    -oo
+
+    The maximum of an empty set is defined to be `-\infty`
+    as seen in this example.
+
+    Computing the dispersion also works over field extensions:
+
+    >>> from sympy import sqrt
+    >>> fp = poly(x**2 + sqrt(5)*x - 1, x, domain='QQ<sqrt(5)>')
+    >>> gp = poly(x**2 + (2 + sqrt(5))*x + sqrt(5), x, domain='QQ<sqrt(5)>')
+    >>> sorted(dispersionset(fp, gp))
+    [2]
+    >>> sorted(dispersionset(gp, fp))
+    [1, 4]
+
+    We can even perform the computations for polynomials
+    having symbolic coefficients:
+
+    >>> from sympy.abc import a
+    >>> fp = poly(4*x**4 + (4*a + 8)*x**3 + (a**2 + 6*a + 4)*x**2 + (a**2 + 2*a)*x, x)
+    >>> sorted(dispersionset(fp))
+    [0, 1]
+
+    See Also
+    ========
+
+    dispersionset
+
+    References
+    ==========
+
+    .. [1] [ManWright94]_
+    .. [2] [Koepf98]_
+    .. [3] [Abramov71]_
+    .. [4] [Man93]_
+    """
+    J = dispersionset(p, q, *gens, **args)
+    if not J:
+        # Definition for maximum of empty set
+        j = S.NegativeInfinity
+    else:
+        j = max(J)
+    return j