# VUMPS, Lapack running error at final outer\_iters **URL:** \ **Category:** DMRG and Numerical Methods\ **Created:** [October 30, 2024, 1:42pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095 "2024-10-30T13:42:53Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![sunam-Jeon](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/sunam-jeon/32/503_2.png) [@sunam-Jeon](https://itensor.discourse.group/u/sunam-Jeon)\ **Post date:** [October 30, 2024, 1:42pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/1 "2024-10-30T13:42:53Z")
I got Lapack error. I set outer\_iters = 5. When running calculations on some machines, it gives a Lapack error. ERROR: LoadError: LAPACKException(22) ---
**Author:** ![ryanlevy](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/ryanlevy/32/150_2.png) [@ryanlevy](https://itensor.discourse.group/u/ryanlevy)\ **Post date:** [October 30, 2024, 2:12pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/2 "2024-10-30T14:12:54Z")
I’m not sure we’ll be able to say much, I suspect its related to this issue: [Occasional `LAPACKException(22)` in `eigsolve` · Issue #57 · Jutho/KrylovKit.jl · GitHub](https://github.com/Jutho/KrylovKit.jl/issues/57) If you have a degeneracy, I would suggest adding a symmetry breaking term and slowly turning it off if possible ---
**Author:** ![sunam-Jeon](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/sunam-jeon/32/503_2.png) [@sunam-Jeon](https://itensor.discourse.group/u/sunam-Jeon)\ **Post date:** [October 30, 2024, 2:40pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/3 "2024-10-30T14:40:55Z")
Thanks but It doesn’t seem to be that kind of issue. When running the calculation on a different computer, it works without any problems. There’s no error when setting `max_vumps_iters=2` and running the calculation. ---
**Author:** ![mtfishman](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/mtfishman/32/11_2.png) [@mtfishman](https://itensor.discourse.group/u/mtfishman)\ **Post date:** [October 30, 2024, 2:44pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/4 "2024-10-30T14:44:30Z")
Different computers can have different floating point roundoffs, which could change the eigenvalue degeneracy enough to cause the eigensolver to either work or not work. ---
**Author:** ![sunam-Jeon](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/sunam-jeon/32/503_2.png) [@sunam-Jeon](https://itensor.discourse.group/u/sunam-Jeon)\ **Post date:** [October 30, 2024, 2:54pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/5 "2024-10-30T14:54:13Z")
Thanks! How can I solve this problem by working around it? Now solver tolerance is set as follows. ‘solver\_tol = (x → x / 100)’ Would it work if I changed this as shown below? ‘solver\_tol = (x → x / 10)’ ---
**Author:** ![mtfishman](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/mtfishman/32/11_2.png) [@mtfishman](https://itensor.discourse.group/u/mtfishman)\ **Post date:** [October 30, 2024, 3:12pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/6 "2024-10-30T15:12:22Z")
I’m not sure, it seems like the source of the error is a bit mysterious, it might help to change the KrylovKit eigensolver parameters or add symmetry breaking terms as Ryan suggested. I think you’ll just have to experiment with things, feel free to update us if you find a robust fix. An alternative could be to try a different eigensolver implementation, like [GitHub - JuliaLinearAlgebra/Arpack.jl: Julia Wrappers for the arpack-ng Fortran library](https://github.com/JuliaLinearAlgebra/Arpack.jl), but that would require changing the source code of ITensorInfiniteMPS.jl (and it may have the same issue as KrylovKit.jl since I think they both call LAPACK anyway for the core diagonalization). ---
**Author:** ![sunam-Jeon](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/sunam-jeon/32/503_2.png) [@sunam-Jeon](https://itensor.discourse.group/u/sunam-Jeon)\ **Post date:** [October 30, 2024, 3:13pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/7 "2024-10-30T15:13:28Z")
Thanks! I will test it ---
**Author:** ![sunam](https://avatars.discourse-cdn.com/v4/letter/s/77aa72/32.png) [@sunam](https://itensor.discourse.group/u/sunam)\ **Post date:** [October 31, 2024, 4:52am UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/8 "2024-10-31T04:52:23Z")
After updating the Julia version to 1.11.1, the error disappeared. Previously, I was using version 1.8.5. ---
**Author:** ![mtfishman](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/mtfishman/32/11_2.png) [@mtfishman](https://itensor.discourse.group/u/mtfishman)\ **Post date:** [October 31, 2024, 1:58pm UTC](https://itensor.discourse.group/t/vumps-lapack-running-error-at-final-outer-iters/2095/9 "2024-10-31T13:58:30Z")
Interesting, I’m not sure why the Julia version would affect this problem but that’s good to know, thanks for the update.