Remove unused diagonalizers and linear solvers from dfoccwave::Tensor2d and dfoccwave::Array2d

[TiborGY]

Description

Much like occ (PR #2679), dfocc also has these functions that are never called anywhere C++-side, and not PSI_API.
This is another shard of the #2642 mega-PR that can be merged independently.

Todos

• Unused code is removed from dfoccwave::Array2d
• Unused code is removed from dfoccwave::Tensor2d

Status

• Ready for review
• Ready for merge

[JonathonMisiewicz]

@loriab, I'm not comfortable merging this in while the dfocc cleanup is ongoing. Your thoughts?

[loriab]

I'm not comfortable merging this in while the dfocc cleanup is ongoing. Your thoughts?

Somehow I had the impression this was in occ, so it was fine. I agree hold off for now.

[TiborGY]

I'm not comfortable merging this in while the dfocc cleanup is ongoing. Your thoughts?

Somehow I had the impression this was in occ, so it was fine. I agree hold off for now.

Sure, no problem. FYI some of the diagonalizer cleanup is blocked until this is in, but I can chip off some other shards.
PS: Homologues of Array2d are present in both occ and dfocc.

[JonathonMisiewicz]

Please focus on other shards. I recommend discussing again once #2669, #2670, and the next PR in that series (not currently pushed, will be about merging in non-FNO methods contributed by Bozkaya's group) are merged in.

[TiborGY]

PR rebased, CI tests are passing.

[JonathonMisiewicz]

I'd like @loriab's opinion before discussing this one, since there's still some dfocc to merge in.

[TiborGY]

I'd like @loriab's opinion before discussing this one, since there's still some dfocc to merge in.

Very well. Please let me know if a decision has been reached. This is blocking the last remaining pieces of the diagonalizer rework saga.

[loriab]

If I'm remembering where I left off and performing the diffs correctly, there's no more changes to be made to those 4 array/tensor files in the dfocc saga. And none of the yet-to-be-PRd code uses davidson, cdsyev, cdgesv, lineq_flin, or lineq_pople. There is new code with diagonalize, though, listed below. If the changes in this PR don't interfere with the calls below, or we can work around them, I think we can release the hold and merge this. Thanks for your patience, @TiborGY.

# HciA is Tensor2d (or sharedptr to it)
cis.cc:          HciA->diagonalize(CciA, EciA, cutoff);

# G is Tensor2d
davidson.cc:    G->diagonalize(init_dim, alpha, lambda, 1e-12, true);
davidson.cc:    G->diagonalize(L, alpha, lambda, 1e-12, true);
davidson.cc:    G->diagonalize(init_dim, alpha, lambda, 1e-12, true);
davidson.cc:    G->diagonalize(L, alpha, lambda, 1e-12, true);
davidson.cc:    G->diagonalize(L, alpha, lambda, 1e-12, true);

# Gamma* and Fock* are Tensor2d
fno.cc:    Gamma_->diagonalize(Tvv_, diag_n_, cutoff_, false);
fno.cc:        FockfvA->diagonalize(UfvA, eigfvA, cutoff_);
fno.cc:        FockvvA->diagonalize(UvvA, eigvvA, cutoff_);
fno.cc:    GammaA_->diagonalize(TvvA_, diag_nA_, cutoff_, false);
fno.cc:    GammaB_->diagonalize(TvvB_, diag_nB_, cutoff_, false);
fno.cc:        FockfvA->diagonalize(UfvA, eigfvA, cutoff_);
fno.cc:        FockvvA->diagonalize(UvvA, eigvvA, cutoff_);
fno.cc:        FockfvB->diagonalize(UfvB, eigfvB, cutoff_);
fno.cc:        FockvvB->diagonalize(UvvB, eigvvB, cutoff_);

# a_opdm, etc. are Matrix
occ_iterations.cc:            a_opdm->diagonalize(aevecs, aevals, descending);
occ_iterations.cc:            a_opdm->diagonalize(aevecs, aevals, descending);
occ_iterations.cc:            b_opdm->diagonalize(bevecs, bevals, descending);

# FockooA, etc. are Tensor2d
semi_canonic.cc:    FockooA->diagonalize(UooA, eigooA, cutoff);
semi_canonic.cc:    FockvvA->diagonalize(UvvA, eigvvA, cutoff);
semi_canonic.cc:        FockooB->diagonalize(UooB, eigooB, cutoff);
semi_canonic.cc:        FockvvB->diagonalize(UvvB, eigvvB, cutoff);

[TiborGY]

Thanks for looking into it. It looks like none of these involve Array2d::diagonalize, so this PR is good on that front. This PR does not touch Matrix::diagonalize, so those calls are safe from it.

But, some Tensor2d::diagonalize calls would indeed fail after this PR. I think the easiest option here is to back out the removal of Tensor2d::diagonalize overloads for now.

FYI, my plan was to eventually change the function signature of Tensor2d::diagonalize after this PR. The init_dim and cutoff arguments have been defunct (as in no-op, unused) for ages. But that can wait until dfocc is no longer in such flux, I can excise sq_rsp while keeping the current interfaces.

[TiborGY]

CI is acting up, but otherwise this is ready

[susilehtola]

Negative LOC always good

[loriab]

lgtm, thanks!