Python解方程demo：sympy

import numpy as np
import sympy as sp


def Equation1( b_1, n_0, n_1, n_2, mode_n ):
    k_0 = 1./1550e-9
    n_eff2 = sp.symbols("n_eff2")

    K_y = (abs(k_0**2*n_1**2 - k_0**2*n_eff2**2))**0.5
    p_y = (abs(k_0**2*n_eff2**2 - k_0**2*n_0**2))**0.5
    q_y = (abs(k_0**2*n_eff2**2 - k_0**2*n_2**2))**0.5

    eq = sp.atan(K_y/p_y) + sp.atan(K_y/q_y) - (K_y*b_1)
    return  sp.nsolve(eq, n_eff2, 3.2)

def Cal_Ex_MODE_neff( a, b_1, b_2, n_0, n_1, n_2, n_3, mode_m, mode_n ):
    print(Equation1(b_1, n_0, n_1, n_2, mode_n))


if __name__ == "__main__":
    n_0 = 3.1
    n_1 = 3.3
    n_2 = 1.44
    n_3 = 3.1
    a = 1.5e-6
    b_1 = 500e-9
    b_2 = 1000e-9

    mode_n = 1
    k_0 = 1./1550e-9

    Cal_Ex_MODE_neff(
        a=a,
        b_1=b_1,
        b_2=b_2,
        n_0=n_0,
        n_1=n_1,
        n_2=n_2,
        n_3=n_3,
        mode_m=0,
        mode_n=0
    )