I think this is at least one bug on 10.5 on linux, attached is testcase
F=Graph(SNIP) #90 vertices
spe=F.spectrum()
a=spe[64]
print("(1):a=",a) #(1) -1.717980512878350? + 0.?e-60*I #XXX imaginary part
print("(2):a=",a,"poly=",a.minpoly()) #(2): -1.717980512878350? poly=
x^4 + 5*x^3 - 19*x - 16 #XXX imaginary part vanishes
"""
1. The spectrum must be real with no imaginary part
2. Why the imaginary part disappears after only print()
"""
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#Author Georgi Guninski 2025-04-14
F=Graph('~?@Y~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Fw~~~yV?~~~{Bh^~~{{FF~~~FC{~~~~Z?B~~~{cQV~~~yQcf~~~{?ZZ~~~w~~F~~~yV~wF~~~_^~c~~~{{~wF~~~ww~{f~~~~Z^{?^~~~cf~HN~~~yQ~{c~~~~_B~uv~~~~w~F~~~~~~xN?~~~~~~{Bc~~~~~~{f?~~~~~~~?{f~~~~~~}u_B~~~~~~{cHN~~~~~~xHcf~~~~~~{?Uv~~~~~~w~~~F~~~w?yV~~ww~~~A^_^~~ff~~{a{{~~~?~~~wkww~~~Q~~~yI~Z^~~_B~~{^~cf~~xH~~~LnyQ~~~QV~~yZ~_B~~|l~~~k~~w~~F~~~w?~~~xN~FF~~wR~~~{B~ff~~{a~~~{f~wF~~~Df~~~?~~Q~~~yI~~~}u~{?^~~b~~~~{c~xH~~~Ln~~~xH~yQ~~~R^~~~{?^|l~~~k~~~~~Fw~~~~?F~~~~~xxFF~~wR~~~~~~b_{~~~cV~~~~~~QwF~~~Df~~~~~~?yV~~~PV~~~~~~lk?^~~b~~~~~~~yQHN~~xl~~~~~~~HIQ~~~R^~~~~~~{?Ln~~|f~~~~~~~w')
#90 vertices
spe=F.spectrum()
a=spe[64]
print("(1):a=",a) #(1) -1.717980512878350? + 0.?e-60*I #XXX imaginary part
print("(2):a=",a,"poly=",a.minpoly()) #(2): -1.717980512878350? poly= x^4 +
5*x^3 - 19*x - 16 #XXX imaginary part vanishes
"""
1. The spectrum must be real with no imaginary part
2. Why the imaginary part disappears after only print()
"""
