234.sagews

from sympy import *
from sympy.matrices import Matrix
from numpy import *
a,b,x=symbols("abx")

Mat_A=Matrix((
(a,b,0,0),
(x,a,b,0),
(x,-2*x,a,b),
(-x**2,-x,x,a),
))
Mat_A

[ a, b, 0, 0] [ x, a, b, 0] [ x, -2*x, a, b] [-x**2, -x, x, a]

h=symbols("h")
eq_1=(Mat_A-eye(4)*h).det()
y=symbols("y")
eq_2=eq_1.subs(h,a+y)
eq_2

-4*a**3*(a + y) + b**2*x**2 + b**3*x**2 + 6*a**2*(a + y)**2 - 4*a*(a + y)**3 + a**4 + (a + y)**4

eq_2.expand()

b**2*x**2 + b**3*x**2 + y**4

lambda=a+sqrt(abs(x)*abs(b)*sqrt(-1*(b+1)))
lambda

Syntax Error: labda