Полином определителя матрицы

import numpy as np
import math 
import matplotlib.pyplot as plt
 
n = 10
 
A = np.random.randint(1, 10, size=(n, n))
 
def sym(matr):
    sym_matr = np.tril(matr) + np.transpose(np.tril(matr, -1))
    return sym_matr
 
A_sym = sym(A)
 
 
 
 
 
def givens_rotation(a):
    for i in range(n - 1):
        for j in range(i + 2, n):               
            
            t = 2*a[i][j]/(a[i][i] - a[j][j])
            phi = 0.5 * math.atan(t)
            c = math.cos(phi)
            s = math.sin(phi)
    
            bii = c*c*a[i][i] + 2*c*s*a[i][j] + s*s*a[j][j]
            bij = s*c*(a[j][j] - a[i][i]) + a[i][j] * (c*c - s*s)
            bjj = s*s*a[i][i] + c*c*a[j][j] - 2*c*s*a[i][j]
            bji = bij;
    
            a[i][i] = bii
            a[i][j] = bij
            a[j][i] = bji
            a[j][j] = bjj
    return np.diagonal(a),np.diagonal(a,1)
 
def polynom(d,c,lam):
    n = len(d) + 1
    p = np.ones(n)
    p[1] = d[0] - lam
    for i in range(2,n):
        p[i] = (d[i-1] - lam)*p[i-1] - (c[i-2]**2)*p[i-2]
    return p 
 
 
 
d,c = givens_rotation(A_sym)
 
def f(lam):             # f(x) = |[A] - lam[E]|
    p = polynom(d,c,lam)
    return p[len(p)-1]
 
lam = np.linspace(0, 20)
y = f(lam)
plt.plot(lam,y)
plt.show()