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/holonomic/numerical.py

@@ -0,0 +1,98 @@
+"""Numerical Methods for Holonomic Functions"""
+
+from sympy.core.sympify import sympify
+from sympy.holonomic.holonomic import DMFsubs
+
+from mpmath import mp
+
+
+def _evalf(func, points, derivatives=False, method='RK4'):
+    """
+    Numerical methods for numerical integration along a given set of
+    points in the complex plane.
+    """
+
+    ann = func.annihilator
+    a = ann.order
+    R = ann.parent.base
+    K = R.get_field()
+
+    if method == 'Euler':
+        meth = _euler
+    else:
+        meth = _rk4
+
+    dmf = [K.new(j.to_list()) for j in ann.listofpoly]
+    red = [-dmf[i] / dmf[a] for i in range(a)]
+
+    y0 = func.y0
+    if len(y0) < a:
+        raise TypeError("Not Enough Initial Conditions")
+    x0 = func.x0
+    sol = [meth(red, x0, points[0], y0, a)]
+
+    for i, j in enumerate(points[1:]):
+        sol.append(meth(red, points[i], j, sol[-1], a))
+
+    if not derivatives:
+        return [sympify(i[0]) for i in sol]
+    else:
+        return sympify(sol)
+
+
+def _euler(red, x0, x1, y0, a):
+    """
+    Euler's method for numerical integration.
+    From x0 to x1 with initial values given at x0 as vector y0.
+    """
+
+    A = sympify(x0)._to_mpmath(mp.prec)
+    B = sympify(x1)._to_mpmath(mp.prec)
+    y_0 = [sympify(i)._to_mpmath(mp.prec) for i in y0]
+    h = B - A
+    f_0 = y_0[1:]
+    f_0_n = 0
+
+    for i in range(a):
+        f_0_n += sympify(DMFsubs(red[i], A, mpm=True))._to_mpmath(mp.prec) * y_0[i]
+    f_0.append(f_0_n)
+
+    return [y_0[i] + h * f_0[i] for i in range(a)]
+
+
+def _rk4(red, x0, x1, y0, a):
+    """
+    Runge-Kutta 4th order numerical method.
+    """
+
+    A = sympify(x0)._to_mpmath(mp.prec)
+    B = sympify(x1)._to_mpmath(mp.prec)
+    y_0 = [sympify(i)._to_mpmath(mp.prec) for i in y0]
+    h = B - A
+
+    f_0_n = 0
+    f_1_n = 0
+    f_2_n = 0
+    f_3_n = 0
+
+    f_0 = y_0[1:]
+    for i in range(a):
+        f_0_n += sympify(DMFsubs(red[i], A, mpm=True))._to_mpmath(mp.prec) * y_0[i]
+    f_0.append(f_0_n)
+
+    f_1 = [y_0[i] + f_0[i]*h/2 for i in range(1, a)]
+    for i in range(a):
+        f_1_n += sympify(DMFsubs(red[i], A + h/2, mpm=True))._to_mpmath(mp.prec) * (y_0[i] + f_0[i]*h/2)
+    f_1.append(f_1_n)
+
+    f_2 = [y_0[i] + f_1[i]*h/2 for i in range(1, a)]
+    for i in range(a):
+        f_2_n += sympify(DMFsubs(red[i], A + h/2, mpm=True))._to_mpmath(mp.prec) * (y_0[i] + f_1[i]*h/2)
+    f_2.append(f_2_n)
+
+    f_3 = [y_0[i] + f_2[i]*h for i in range(1, a)]
+    for i in range(a):
+        f_3_n += sympify(DMFsubs(red[i], A + h, mpm=True))._to_mpmath(mp.prec) * (y_0[i] + f_2[i]*h)
+    f_3.append(f_3_n)
+
+    return [y_0[i] + h*(f_0[i]+2*f_1[i]+2*f_2[i]+f_3[i])/6 for i in range(a)]