chore: 添加虚拟环境到仓库

- 添加 backend_service/venv 虚拟环境
- 包含所有Python依赖包
- 注意：虚拟环境约393MB，包含12655个文件

backend_service/venv/lib/python3.13/site-packages/sympy/series/approximants.py

@@ -0,0 +1,103 @@
+from sympy.core.singleton import S
+from sympy.core.symbol import Symbol
+from sympy.polys.polytools import lcm
+from sympy.utilities import public
+
+@public
+def approximants(l, X=Symbol('x'), simplify=False):
+    """
+    Return a generator for consecutive Pade approximants for a series.
+    It can also be used for computing the rational generating function of a
+    series when possible, since the last approximant returned by the generator
+    will be the generating function (if any).
+
+    Explanation
+    ===========
+
+    The input list can contain more complex expressions than integer or rational
+    numbers; symbols may also be involved in the computation. An example below
+    show how to compute the generating function of the whole Pascal triangle.
+
+    The generator can be asked to apply the sympy.simplify function on each
+    generated term, which will make the computation slower; however it may be
+    useful when symbols are involved in the expressions.
+
+    Examples
+    ========
+
+    >>> from sympy.series import approximants
+    >>> from sympy import lucas, fibonacci, symbols, binomial
+    >>> g = [lucas(k) for k in range(16)]
+    >>> [e for e in approximants(g)]
+    [2, -4/(x - 2), (5*x - 2)/(3*x - 1), (x - 2)/(x**2 + x - 1)]
+
+    >>> h = [fibonacci(k) for k in range(16)]
+    >>> [e for e in approximants(h)]
+    [x, -x/(x - 1), (x**2 - x)/(2*x - 1), -x/(x**2 + x - 1)]
+
+    >>> x, t = symbols("x,t")
+    >>> p=[sum(binomial(k,i)*x**i for i in range(k+1)) for k in range(16)]
+    >>> y = approximants(p, t)
+    >>> for k in range(3): print(next(y))
+    1
+    (x + 1)/((-x - 1)*(t*(x + 1) + (x + 1)/(-x - 1)))
+    nan
+
+    >>> y = approximants(p, t, simplify=True)
+    >>> for k in range(3): print(next(y))
+    1
+    -1/(t*(x + 1) - 1)
+    nan
+
+    See Also
+    ========
+
+    sympy.concrete.guess.guess_generating_function_rational
+    mpmath.pade
+    """
+    from sympy.simplify import simplify as simp
+    from sympy.simplify.radsimp import denom
+    p1, q1 = [S.One], [S.Zero]
+    p2, q2 = [S.Zero], [S.One]
+    while len(l):
+        b = 0
+        while l[b]==0:
+            b += 1
+            if b == len(l):
+                return
+        m = [S.One/l[b]]
+        for k in range(b+1, len(l)):
+            s = 0
+            for j in range(b, k):
+                s -= l[j+1] * m[b-j-1]
+            m.append(s/l[b])
+        l = m
+        a, l[0] = l[0], 0
+        p = [0] * max(len(p2), b+len(p1))
+        q = [0] * max(len(q2), b+len(q1))
+        for k in range(len(p2)):
+            p[k] = a*p2[k]
+        for k in range(b, b+len(p1)):
+            p[k] += p1[k-b]
+        for k in range(len(q2)):
+            q[k] = a*q2[k]
+        for k in range(b, b+len(q1)):
+            q[k] += q1[k-b]
+        while p[-1]==0: p.pop()
+        while q[-1]==0: q.pop()
+        p1, p2 = p2, p
+        q1, q2 = q2, q
+
+        # yield result
+        c = 1
+        for x in p:
+            c = lcm(c, denom(x))
+        for x in q:
+            c = lcm(c, denom(x))
+        out = ( sum(c*e*X**k for k, e in enumerate(p))
+              / sum(c*e*X**k for k, e in enumerate(q)) )
+        if simplify:
+            yield(simp(out))
+        else:
+            yield out
+    return