# An Error while running DMRG

Hi, I am using DMRG in ITensor.
I have created an additional site object and related operators for a one dimensional system.
I do not get any error while running DMRG without any conservation.
But I am getting error while running DMRG with conserving quantum number.
The error is the following,
“ERROR: LoadError: Eigen currently only supports block diagonal matrices.”
The source of this error is line 196 of file “linearalgebra.jl” which is a part of ITensor package.
If one can help me, about the meaning of the error, I might be able to resolve the problem.

Can it be related with the ordering of basis according to quantum numbers? Because in site function I have multiple basises with degenerate quantum numbers. I have printed the MPO for Hamiltonian for three site system, which might be helpful for guessing the problem,

MPO
1: QN() => 1
2: QN(“Sz”,0) => 2
3: QN(“Sz”,1) => 3
4: QN(“Sz”,-1) => 3
5: QN(“Sz”,0) => 1, (dim=9|id=47|“Site,bondoperator1,n=1”)’
1: QN(“Sz”,0) => 1
2: QN(“Sz”,0) => 1
3: QN(“Sz”,0) => 1
4: QN(“Sz”,-1) => 1
5: QN(“Sz”,-1) => 1
6: QN(“Sz”,1) => 1
7: QN(“Sz”,1) => 1
8: QN(“Sz”,-2) => 1
9: QN(“Sz”,2) => 1, (dim=9|id=47|“Site,bondoperator1,n=1”)
1: QN(“Sz”,0) => 1
2: QN(“Sz”,0) => 1
3: QN(“Sz”,0) => 1
4: QN(“Sz”,-1) => 1
5: QN(“Sz”,-1) => 1
6: QN(“Sz”,1) => 1
7: QN(“Sz”,1) => 1
8: QN(“Sz”,-2) => 1
9: QN(“Sz”,2) => 1)
1: QN() => 1
2: QN(“Sz”,0) => 2
3: QN(“Sz”,1) => 3
4: QN(“Sz”,-1) => 3
1: QN() => 1
2: QN(“Sz”,0) => 2
3: QN(“Sz”,1) => 3
4: QN(“Sz”,-1) => 3
5: QN(“Sz”,0) => 1, (dim=9|id=694|“Site,bondoperator1,n=2”)’
1: QN(“Sz”,0) => 1
2: QN(“Sz”,0) => 1
3: QN(“Sz”,0) => 1
4: QN(“Sz”,-1) => 1
5: QN(“Sz”,-1) => 1
6: QN(“Sz”,1) => 1
7: QN(“Sz”,1) => 1
8: QN(“Sz”,-2) => 1
9: QN(“Sz”,2) => 1, (dim=9|id=694|“Site,bondoperator1,n=2”)
1: QN(“Sz”,0) => 1
2: QN(“Sz”,0) => 1
3: QN(“Sz”,0) => 1
4: QN(“Sz”,-1) => 1
5: QN(“Sz”,-1) => 1
6: QN(“Sz”,1) => 1
7: QN(“Sz”,1) => 1
8: QN(“Sz”,-2) => 1
9: QN(“Sz”,2) => 1)
1: QN() => 1
2: QN(“Sz”,0) => 2
3: QN(“Sz”,1) => 3
4: QN(“Sz”,-1) => 3
5: QN(“Sz”,0) => 1, (dim=9|id=404|“Site,bondoperator1,n=3”)’
1: QN(“Sz”,0) => 1
2: QN(“Sz”,0) => 1
3: QN(“Sz”,0) => 1
4: QN(“Sz”,-1) => 1
5: QN(“Sz”,-1) => 1
6: QN(“Sz”,1) => 1
7: QN(“Sz”,1) => 1
8: QN(“Sz”,-2) => 1
9: QN(“Sz”,2) => 1, (dim=9|id=404|“Site,bondoperator1,n=3”)
1: QN(“Sz”,0) => 1
2: QN(“Sz”,0) => 1
3: QN(“Sz”,0) => 1
4: QN(“Sz”,-1) => 1
5: QN(“Sz”,-1) => 1
6: QN(“Sz”,1) => 1
7: QN(“Sz”,1) => 1
8: QN(“Sz”,-2) => 1
9: QN(“Sz”,2) => 1)