Fix Jordan normal form (#1280)

thofma · Nov 9, 2023 · 829741c · 829741c
1 parent dd1b63c
commit 829741c
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diff --git a/src/Misc/jordan.jl b/src/Misc/jordan.jl
@@ -81,6 +81,7 @@ function closure_with_pol(v::MatElem{T}, M::MatElem{T}) where T <: FieldElem
   E = rref(v)[2]
   w = v*M
   res = Hecke.cleanvect(E, w)
+  v = deepcopy(v) # the output should not "share" entries with the input
   while !iszero(res)
     v = vcat(v, w)
     E = vcat(E, res)

diff --git a/test/Misc/jordan_test.jl b/test/Misc/jordan_test.jl
@@ -51,6 +51,12 @@
   @test CF == C
   @test TM * C * inv(TM) == CF
 
+  # Issue #1279
+  K, _ = number_field(x^2 - 2)
+  M = matrix(K, [ 0 1 1; 1//2 0 0 ; 1//2 0 0 ])
+  J, S = jordan_normal_form(M)
+  @test J == S*M*inv(S)
+  @test Set([ J[1, 1], J[2, 2], J[3, 3] ]) == Set([ K(), K(1), K(-1) ])
 end
 
 @testset "Spectrum and eigenspaces" begin