Source code for sympy.core.mod

from __future__ import print_function, division

from .function import Function

[docs]class Mod(Function): """Represents a modulo operation on symbolic expressions. Receives two arguments, dividend p and divisor q. The convention used is the same as Python's: the remainder always has the same sign as the divisor. Examples ======== >>> from sympy.abc import x, y >>> x**2 % y Mod(x**2, y) >>> _.subs({x: 5, y: 6}) 1 """ nargs = 2 @classmethod def eval(cls, p, q): from sympy.core.add import Add from sympy.core.mul import Mul from sympy.core.singleton import S from sympy.core.exprtools import gcd_terms from sympy.polys.polytools import gcd def doit(p, q): """Try to return p % q if both are numbers or +/-p is known to be less than q. """ if p == q or p == -q or p.is_Pow and p.exp.is_Integer and p.base == q: return S.Zero if p.is_Number and q.is_Number: return (p % q) # by ratio r = p/q try: d = int(r) except TypeError: pass else: if type(d) is int: rv = p - d*q if (rv*q < 0) is True: rv += q return rv # by differencec d = p - q if d.is_negative: if q.is_negative: return d elif q.is_positive: return p rv = doit(p, q) if rv is not None: return rv # denest if p.func is cls: # easy qinner = p.args[1] if qinner == q: return p # XXX other possibilities? # extract gcd; any further simplification should be done by the user G = gcd(p, q) if G is not S.One: p, q = [ gcd_terms(i/G, clear=False, fraction=False) for i in (p, q)] pwas, qwas = p, q # simplify terms # (x + y + 2) % x -> Mod(y + 2, x) if p.is_Add: args = [] for i in p.args: a = cls(i, q) if a.count(cls) > i.count(cls): args.append(i) else: args.append(a) if args != list(p.args): p = Add(*args) else: # handle coefficients if they are not Rational # since those are not handled by factor_terms # e.g. Mod(.6*x, .3*y) -> 0.3*Mod(2*x, y) cp, p = p.as_coeff_Mul() cq, q = q.as_coeff_Mul() ok = False if not cp.is_Rational or not cq.is_Rational: r = cp % cq if r == 0: G *= cq p *= int(cp/cq) ok = True if not ok: p = cp*p q = cq*q # simple -1 extraction if p.could_extract_minus_sign() and q.could_extract_minus_sign(): G, p, q = [-i for i in (G, p, q)] # check again to see if p and q can now be handled as numbers rv = doit(p, q) if rv is not None: return rv*G # put 1.0 from G on inside if G.is_Float and G == 1: p *= G return cls(p, q, evaluate=False) elif G.is_Mul and G.args[0].is_Float and G.args[0] == 1: p = G.args[0]*p G = Mul._from_args(G.args[1:]) return G*cls(p, q, evaluate=(p, q) != (pwas, qwas))