Description
When using cytnx.linalg.Lanczos with a LinOp that operates on symmetric UniTensors, the eigenvalues results differ from the non-symmetric case, even when the underlying data is equivalent. While exact diagonalization (cytnx.linalg.Eig) remains consistent across both symmetric and non-symmetric representations, the iterative Lanczos solver exhibits significant instability when symmetry is involved.
This instability appears to be contraction-order dependent, suggesting a potential bug in how the LinOp interface or the Lanczos solver handles symmetric sectors during iterative matrix-vector multiplications.
Reproduction Codes
show_symm_Lanczos_issue.html
show_symm_Lanczos_issue.ipynb
Eigenvalues results
Environment
Cytnx Version: 1.0.1
Description
When using
cytnx.linalg.Lanczoswith aLinOpthat operates on symmetric UniTensors, the eigenvalues results differ from the non-symmetric case, even when the underlying data is equivalent. While exact diagonalization (cytnx.linalg.Eig) remains consistent across both symmetric and non-symmetric representations, the iterative Lanczos solver exhibits significant instability when symmetry is involved.This instability appears to be contraction-order dependent, suggesting a potential bug in how the
LinOpinterface or the Lanczos solver handles symmetric sectors during iterative matrix-vector multiplications.Reproduction Codes
show_symm_Lanczos_issue.html
show_symm_Lanczos_issue.ipynb
Eigenvalues results
Environment
Cytnx Version: 1.0.1