def eval_sum_symbolic(f, limits): from sympy.functions import harmonic, bernoulli f_orig = f (i, a, b) = limits if not f.has(i): return f*(b - a + 1) # Linearity if f.is_Mul: L, R = f.as_two_terms() if not L.has(i): sR = eval_sum_symbolic(R, (i, a, b)) if sR: return L*sR if not R.has(i): sL = eval_sum_symbolic(L, (i, a, b)) if sL: return R*sL try: f = apart(f, i) # see if it becomes an Add except PolynomialError: pass if f.is_Add: L, R = f.as_two_terms() lrsum = telescopic(L, R, (i, a, b)) if lrsum: return lrsum lsum = eval_sum_symbolic(L, (i, a, b)) rsum = eval_sum_symbolic(R, (i, a, b)) if None not in (lsum, rsum): r = lsum + rsum if not r is S.NaN: return r # Polynomial terms with Faulhaber's formula n = Wild('n') result = f.match(i**n) if result is not None: n = result[n] if n.is_Integer: if n >= 0: if (b is S.Infinity and not a is S.NegativeInfinity) or \ (a is S.NegativeInfinity and not b is S.Infinity): return S.Infinity return ((bernoulli(n + 1, b + 1) - bernoulli(n + 1, a))/(n + 1)).expand() elif a.is_Integer and a >= 1: if n == -1: return harmonic(b) - harmonic(a - 1) else: return harmonic(b, abs(n)) - harmonic(a - 1, abs(n)) if not (a.has(S.Infinity, S.NegativeInfinity) or b.has(S.Infinity, S.NegativeInfinity)): # Geometric terms c1 = Wild('c1', exclude=[i]) c2 = Wild('c2', exclude=[i]) c3 = Wild('c3', exclude=[i]) wexp = Wild('wexp') # Here we first attempt powsimp on f for easier matching with the # exponential pattern, and attempt expansion on the exponent for easier # matching with the linear pattern. e = f.powsimp().match(c1 ** wexp) if e is not None: e_exp = e.pop(wexp).expand().match(c2*i + c3) if e_exp is not None: e.update(e_exp) if e is not None: p = (c1**c3).subs(e) q = (c1**c2).subs(e) r = p*(q**a - q**(b + 1))/(1 - q) l = p*(b - a + 1) return Piecewise((l, Eq(q, S.One)), (r, True)) r = gosper_sum(f, (i, a, b)) if isinstance(r, (Mul,Add)): from sympy import ordered, Tuple non_limit = r.free_symbols - Tuple(*limits[1:]).free_symbols den = denom(together(r)) den_sym = non_limit & den.free_symbols args = [] for v in ordered(den_sym): try: s = solve(den, v) m = Eq(v, s[0]) if s else S.false if m != False: args.append((Sum(f_orig.subs(*m.args), limits).doit(), m)) break except NotImplementedError: continue args.append((r, True)) return Piecewise(*args) if not r in (None, S.NaN): return r h = eval_sum_hyper(f_orig, (i, a, b)) if h is not None: return h factored = f_orig.factor() if factored != f_orig: return eval_sum_symbolic(factored, (i, a, b))