Rotate

Matrix.Rotate($M$,$U$) makes the matrix transformation $U^* . M . U^T$.

Example.Quanty

M = Matrix.New({{1,I,2,I},
                {-I,1,I,2},
                {2,-I,4,I},
                {-I,2,-I,4}})
val, fun = Matrix.Eigensystem(M)
 
Mdiag = Chop(Rotate(M,fun))
print(Mdiag)

{ { -1.1401 ,  0      ,  0      ,  0      } ,
  {  0      ,  0.6972 ,  0      ,  0      } ,
  {  0      ,  0      ,  4.3028 ,  0      } ,
  {  0      ,  0      ,  0      ,  6.1401 } }