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Faster eigensolver for the benchmark #18

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dcd9fa8
Add an interface to DSYGVX
certik Oct 20, 2023
44d32e9
Use dsygvx
certik Oct 20, 2023
aa40851
Simplify
certik Oct 20, 2023
3284be8
Hardwire accurate_eigensolver = .false.
certik Oct 20, 2023
a9ce4b2
Do not copy matrices
certik Oct 20, 2023
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2 changes: 1 addition & 1 deletion src/dirac.f90
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Expand Up @@ -234,7 +234,7 @@ subroutine Ffunc(x, y, eng)
real(dp) :: E_dirac_shift
integer :: idx
logical :: accurate_eigensolver
accurate_eigensolver = .true.
accurate_eigensolver = .false.
iter = iter + 1
print *, "SCF iteration:", iter
Vin = reshape(x, shape(Vin))
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12 changes: 12 additions & 0 deletions src/lapack.f90
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Expand Up @@ -77,6 +77,18 @@ SUBROUTINE DSYGVD( ITYPE, JOBZ, UPLO, N, A, LDA, B, LDB, W, WORK, &
REAL(dp) A( LDA, * ), B( LDB, * ), W( * ), WORK( * )
END SUBROUTINE

SUBROUTINE DSYGVX( ITYPE, JOBZ, RANGE, UPLO, N, A, LDA, B, LDB, &
VL, VU, IL, IU, ABSTOL, M, W, Z, LDZ, WORK, &
LWORK, IWORK, IFAIL, INFO )
import :: dp
CHARACTER JOBZ, RANGE, UPLO
INTEGER IL, INFO, ITYPE, IU, LDA, LDB, LDZ, LWORK, M, N
REAL(dp) ABSTOL, VL, VU
INTEGER IFAIL( * ), IWORK( * )
REAL(dp) A( LDA, * ), B( LDB, * ), W( * ), WORK( * ), &
Z( LDZ, * )
END SUBROUTINE

REAL(dp) FUNCTION DLAMCH( CMACH )
import :: dp
CHARACTER CMACH
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27 changes: 21 additions & 6 deletions src/linalg.f90
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@@ -1,6 +1,6 @@
module linalg
use types, only: dp
use lapack, only: dsyevd, dsygvd, dgesv
use lapack, only: dsyevd, dsygvd, dgesv, dsygvx
implicit none
private
public eigh, solve
Expand All @@ -24,8 +24,10 @@ subroutine deigh_generalized(Am, Bm, lam, c)
integer :: n
! lapack variables
integer :: lwork, liwork, info
integer, allocatable :: iwork(:)
real(dp), allocatable :: Bmt(:,:), work(:)
integer, allocatable :: iwork(:), ifail(:)
real(dp), allocatable :: Bmt(:,:), work(:), Z(:,:), Amt(:,:)
integer :: il, iu, M
real(dp) :: abstol

! solve
n = size(Am,1)
Expand All @@ -34,9 +36,22 @@ subroutine deigh_generalized(Am, Bm, lam, c)
call assert_shape(c, [n, n], "eigh", "c")
lwork = 1 + 6*n + 2*n**2
liwork = 3 + 5*n
allocate(Bmt(n,n), work(lwork), iwork(liwork))
c = Am; Bmt = Bm ! Bmt temporaries overwritten by dsygvd
call dsygvd(1,'V','L',n,c,n,Bmt,n,lam,work,lwork,iwork,liwork,info)
allocate(work(lwork), iwork(liwork))
allocate(ifail(n))
!call dsygvd(1,'V','L',n,c,n,Bmt,n,lam,work,lwork,iwork,liwork,info)
il = 1
iu = 7
M = iu-il+1
allocate(z(n,M))
abstol = 1e-4_dp
call dsygvx(1,'V','I','L',n,Am,n,Bm,n, &
0._dp, 0._dp, 1, 7, abstol, M, lam, c, n, work, &
lwork, iwork, ifail, info)
!SUBROUTINE DSYGVD( ITYPE, JOBZ, UPLO, N, A, LDA, B, LDB, W, WORK, &
! LWORK, IWORK, LIWORK, INFO )
!SUBROUTINE DSYGVX( ITYPE, JOBZ, RANGE, UPLO, N, A, LDA, B, LDB, &
! VL, VU, IL, IU, ABSTOL, M, W, Z, LDZ, WORK, &
! LWORK, IWORK, IFAIL, INFO )
if (info /= 0) then
print *, "dsygvd returned info =", info
if (info < 0) then
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