expr not of form a*x**b:

问题遇到的现象和发生背景

用代码块功能插入代码，请勿粘贴截图

import numpy as np
import sympy as sp
from scipy import integrate

Vi = 350.0
Vj = 310.0
lamb_xy = 0.035
lamb_z = 0.015
Vij = 87.7
z = 1.0
sigma = 0.0147
sigmaz = np.sqrt(2) * sigma
sigmay = np.sqrt(2) * sigma
sigmax = np.sqrt(2) * sigma
print(sigmax)
P1 = 0.05
P2 = 0.95
t_min = 1 / 36
t_max = 1 / 20
t_av = 1 / 24

Hlong = 15
Casex = 1 / (np.sqrt(2 * np.pi) * sigmax)
Casey = 1 / (np.sqrt(2 * np.pi) * sigmay)
Casez = 1 / (np.sqrt(2 * np.pi) * sigmaz)
Case = (1 + (np.pi * lamb_xy * z) / (4 * lamb_z * Vij))
lamb_f = 1 / (t_av - t_min)
Ti = Hlong / Vj
# 碰撞概率
if Ti < t_min:
    CP_av = 0
    CR = 0
else:

    Ti = Ti + t_av
    P_y = lambda r: Casey * np.exp (-r ** 2 / (2 * sigmay ** 2))
    P_y = integrate.quad(P_y, -lamb_xy, lamb_xy)
    P_z = lambda r: Casez * np.exp (-r ** 2 / (2 * sigmaz ** 2))
    P_z = integrate.quad(P_z, -lamb_z, lamb_z)
    t=sp.symbols('t')
    r=sp.symbols('r')
    t_d=sp.symbols('t_d')
    S_x = Vi * (t + t_av) - Vj * t


    #有问题
    P_x = Casex * sp.exp(-(r - S_x) ** 2 / (2 * sigmax ** 2))
    P_x = sp.integrate(P_x, (r,-lamb_xy, lamb_xy))
    P = P_x * P_y[0] * P_z[0] * Case
    print(P_x)
    F = lamb_f * sp.exp(-lamb_f * (t_d - t_min))

    CP = 1 / (Ti - t_d) * sp.integrate(P, (t, 0, (Hlong - 1 / 36 * Vi) / Vi))
    print(CP)
    CP = P1 * P2 * CP * F
    CP_av = abs(sp.integrate(CP, (t_d, t_min, t_max)))
    CR = 2 * CP_av / (P1 * (Hlong - 1 / 36 * Vi) / Vi + P2 * Ti)

运行结果及报错内容

sympy.integrals.meijerint._CoeffExpValueError: expr not of form a*x**b: 11.1044776119403