Off[General::precw];​​a=b=1
3
;​​r=0.01;​​​​
p
r
=
m
2
b
4
Cosh[r]
2m-2
Tanh[r]
+(1-
2
a
-
2
b
)
2m
Tanh[r]
2
Cosh[r]
0
0
ba
3
Cosh[r]
m+1
2m
Tanh[r]
0
2
a
2
Cosh[r]
2m
Tanh[r]
0
0
0
0
(1-
2
a
-
2
b
)
2m+2
Tanh[r]
2
Cosh[r]
+
(m+1)
2
b
4
Cosh[r]
2m
Tanh[r]
0
ab
3
Cosh[r]
m+1
2m
Tanh[r]
0
0
2
a
2
Cosh[r]
2m+2
Tanh[r]
;​​​​
pp
r
=
p
r
.
p
r
;​​
eigen
r
=Eigenvalues[
pp
r
];​​
seigen
r
=Sqrt[
eigen
r
];​​
Ne
r
=Re[NSum[Total[
seigen
r
],{m,0,Infinity}]]-1​​​​
0.745303