def solve_univariate_inequality(expr, gen, assume=True, relational=True): """Solves a real univariate inequality. Examples ======== >>> from sympy.solvers.inequalities import solve_univariate_inequality >>> from sympy.core.symbol import Symbol >>> x = Symbol('x', real=True) >>> solve_univariate_inequality(x**2 >= 4, x) Or(x <= -2, x >= 2) >>> solve_univariate_inequality(x**2 >= 4, x, relational=False) (-oo, -2] U [2, oo) """ # Implementation for continous functions from sympy.solvers.solvers import solve solns = solve(expr.lhs - expr.rhs, gen, assume=assume) oo = S.Infinity start = -oo sol_sets = [S.EmptySet] for x in sorted(s for s in solns if s.is_real): end = x if expr.subs(gen, (start + end) / 2 if start != -oo else end - 1): sol_sets.append(Interval(start, end, True, True)) if expr.subs(gen, x): sol_sets.append(FiniteSet(x)) start = end end = oo if expr.subs(gen, start + 1): sol_sets.append(Interval(start, end, True, True)) rv = Union(*sol_sets) return rv if not relational else rv.as_relational(gen)
def solve_poly_inequality(poly, rel): """Solve a polynomial inequality with rational coefficients. """ reals, intervals = poly.real_roots(multiple=False), [] if rel == '==': for root, _ in reals: interval = Interval(root, root) intervals.append(interval) elif rel == '!=': left = S.NegativeInfinity for right, _ in reals + [(S.Infinity, 1)]: interval = Interval(left, right, True, True) intervals.append(interval) left = right else: if poly.LC() > 0: sign = +1 else: sign = -1 eq_sign, equal = None, False if rel == '>': eq_sign = +1 elif rel == '<': eq_sign = -1 elif rel == '>=': eq_sign, equal = +1, True elif rel == '<=': eq_sign, equal = -1, True else: raise ValueError("'%s' is not a valid relation" % rel) right, right_open = S.Infinity, True for left, multiplicity in reversed(reals): if multiplicity % 2: if sign == eq_sign: intervals.insert( 0, Interval(left, right, not equal, right_open)) sign, right, right_open = -sign, left, not equal else: if sign == eq_sign and not equal: intervals.insert(0, Interval(left, right, True, right_open)) right, right_open = left, True elif sign != eq_sign and equal: intervals.insert(0, Interval(left, left)) if sign == eq_sign: intervals.insert( 0, Interval(S.NegativeInfinity, right, True, right_open)) return intervals
def interval_evalf(interval): """Proper implementation of evalf() on Interval. Examples ======== >>> from sympy.core import Interval, Symbol >>> from sympy.solvers.inequalities import interval_evalf >>> interval_evalf(Interval(1, 3)) [1.0, 3.0] >>> x = Symbol('x', real=True) >>> interval_evalf(Interval(2*x, x - 5)) [2.0*x, x - 5.0] """ return Interval(interval.left.evalf(), interval.right.evalf(), left_open=interval.left_open, right_open=interval.right_open)
def deltasummation(f, limit, no_piecewise=False): """ Handle summations containing a KroneckerDelta. The idea for summation is the following: - If we are dealing with a KroneckerDelta expression, i.e. KroneckerDelta(g(x), j), we try to simplify it. If we could simplify it, then we sum the resulting expression. We already know we can sum a simplified expression, because only simple KroneckerDelta expressions are involved. If we couldn't simplify it, there are two cases: 1) The expression is a simple expression: we return the summation, taking care if we are dealing with a Derivative or with a proper KroneckerDelta. 2) The expression is not simple (i.e. KroneckerDelta(cos(x))): we can do nothing at all. - If the expr is a multiplication expr having a KroneckerDelta term: First we expand it. If the expansion did work, then we try to sum the expansion. If not, we try to extract a simple KroneckerDelta term, then we have two cases: 1) We have a simple KroneckerDelta term, so we return the summation. 2) We didn't have a simple term, but we do have an expression with simplified KroneckerDelta terms, so we sum this expression. Examples ======== >>> from sympy import oo >>> from sympy.abc import i, j, k >>> from sympy.concrete.delta import deltasummation >>> from sympy import KroneckerDelta, Piecewise >>> deltasummation(KroneckerDelta(i, k), (k, -oo, oo)) 1 >>> deltasummation(KroneckerDelta(i, k), (k, 0, oo)) Piecewise((1, i >= 0), (0, True)) >>> deltasummation(KroneckerDelta(i, k), (k, 1, 3)) Piecewise((1, And(1 <= i, i <= 3)), (0, True)) >>> deltasummation(k*KroneckerDelta(i, j)*KroneckerDelta(j, k), (k, -oo, oo)) j*KroneckerDelta(i, j) >>> deltasummation(j*KroneckerDelta(i, j), (j, -oo, oo)) i >>> deltasummation(i*KroneckerDelta(i, j), (i, -oo, oo)) j See Also ======== deltaproduct sympy.functions.special.tensor_functions.KroneckerDelta sympy.concrete.sums.summation """ from sympy.concrete.summations import summation from sympy.solvers import solve if ((limit[2] - limit[1]) < 0) is True: return S.Zero if not f.has(KroneckerDelta): return summation(f, limit) x = limit[0] g = _expand_delta(f, x) if g.is_Add: return piecewise_fold( g.func(*[deltasummation(h, limit, no_piecewise) for h in g.args])) # try to extract a simple KroneckerDelta term delta, expr = _extract_delta(g, x) if not delta: return summation(f, limit) solns = solve(delta.args[0] - delta.args[1], x) if len(solns) == 0: return S.Zero elif len(solns) != 1: return Sum(f, limit) value = solns[0] if no_piecewise: return expr.subs(x, value) return Piecewise( (expr.subs(x, value), Interval(*limit[1:3]).as_relational(value)), (S.Zero, True) )
def solve_poly_inequality(poly, rel): """Solve a polynomial inequality with rational coefficients. Examples ======== >>> from sympy import Poly >>> from sympy.abc import x >>> from sympy.solvers.inequalities import solve_poly_inequality >>> solve_poly_inequality(Poly(x, x, domain='ZZ'), '==') [{0}] >>> solve_poly_inequality(Poly(x**2 - 1, x, domain='ZZ'), '!=') [(-oo, -1), (-1, 1), (1, oo)] >>> solve_poly_inequality(Poly(x**2 - 1, x, domain='ZZ'), '==') [{-1}, {1}] See Also ======== solve_poly_inequalities """ reals, intervals = poly.real_roots(multiple=False), [] if rel == '==': for root, _ in reals: interval = Interval(root, root) intervals.append(interval) elif rel == '!=': left = S.NegativeInfinity for right, _ in reals + [(S.Infinity, 1)]: interval = Interval(left, right, True, True) intervals.append(interval) left = right else: if poly.LC() > 0: sign = +1 else: sign = -1 eq_sign, equal = None, False if rel == '>': eq_sign = +1 elif rel == '<': eq_sign = -1 elif rel == '>=': eq_sign, equal = +1, True elif rel == '<=': eq_sign, equal = -1, True else: raise ValueError("'%s' is not a valid relation" % rel) right, right_open = S.Infinity, True reals.sort(key=lambda w: w[0], reverse=True) for left, multiplicity in reals: if multiplicity % 2: if sign == eq_sign: intervals.insert( 0, Interval(left, right, not equal, right_open)) sign, right, right_open = -sign, left, not equal else: if sign == eq_sign and not equal: intervals.insert( 0, Interval(left, right, True, right_open)) right, right_open = left, True elif sign != eq_sign and equal: intervals.insert(0, Interval(left, left)) if sign == eq_sign: intervals.insert( 0, Interval(S.NegativeInfinity, right, True, right_open)) return intervals
def interval_evalf(interval): """Proper implementation of evalf() on Interval. """ return Interval(interval.left.evalf(), interval.right.evalf(), left_open=interval.left_open, right_open=interval.right_open)