fast restore symmetry

src/utils/linear_algebra.irp.f

@@ -1690,6 +1690,19 @@ subroutine restore_symmetry(m,n,A,LDA,thresh)
   thresh2 = dsqrt(thresh)
   call nullify_small_elements(m,n,A,LDA,thresh)
 
+  ! Debug
+  !double precision, allocatable :: B(:,:)
+  !double precision :: max_diff, ti,tf
+  !allocate(B(m,n))
+  !B = A
+  !call wall_time(ti)
+  !call restore_symmetry_fast(m,n,B,LDA,thresh)
+  !call wall_time(tf)
+  !print*,''
+  !print*,'Restore_symmetry'
+  !print*,'Fast version:',tf-ti,'s'
+  !call wall_time(ti)
+
 !  if (.not.restore_symm) then
 !    return
 !  endif
@@ -1749,23 +1762,128 @@ subroutine restore_symmetry(m,n,A,LDA,thresh)
     enddo
   enddo
 
+  ! Debug
+  !call wall_time(tf)
+  !print*,'Old version:',tf-ti,'s'
+
+  !max_diff = 0d0
+  !do j = 1, n
+  !  do i = 1, n
+  !    if (dabs(A(i,j)-B(i,j)) > max_diff) then
+  !      max_diff = dabs(A(i,j)-B(i,j))
+  !    endif
+  !  enddo
+  !enddo
+  !print*,'Max diff:', max_diff
+  !deallocate(B)
+
 end
 
+subroutine restore_symmetry_fast(m,n,A,LDA,thresh)
 
+  implicit none
 
+  BEGIN_DOC
+  ! Tries to find the matrix elements that are the same, and sets them
+  ! to the average value.
+  ! If restore_symm is False, only nullify small elements
+  END_DOC
 
+  integer, intent(in) :: m,n,LDA
+  double precision, intent(inout) :: A(LDA,n)
+  double precision, intent(in) :: thresh
 
+  double precision, allocatable :: copy(:), copy_sign(:)
+  integer, allocatable :: key(:)
+  integer :: sze, pi, pf, idx, i,j,k
+  double precision :: average, val, thresh2
 
+  thresh2 = dsqrt(thresh)
+  call nullify_small_elements(m,n,A,LDA,thresh)
  
+  sze = m * n
 
+  allocate(copy(sze),copy_sign(sze),key(sze))
   
+  ! Copy to 1D
+  !$OMP PARALLEL &
+  !$OMP SHARED(A,m,n,sze,copy_sign,copy,key) &
+  !$OMP PRIVATE(i,j,k) &
+  !$OMP DEFAULT(NONE)
+  !$OMP DO
+  do j = 1, n
+    do i = 1, m
+      copy(i+(j-1)*m) = A(i,j)
+    enddo
+  enddo
+  !$OMP END DO
+  ! Copy sign
+  !$OMP DO
+  do i = 1,sze
+    copy_sign(i) = sign(1d0,copy(i))
+    copy(i) = dabs(copy(i))
+  enddo
+  !$OMP END DO NOWAIT
+  ! Keys
+  !$OMP DO
+  do i = 1, sze
+   key(i) = i
+  enddo
+  !$OMP END DO
+  !$OMP END PARALLEL
 
+  ! Sort
+  call dsort(copy,key,sze)
 
+  ! Symmetrize
+  i = 1
+  do while(i < sze)
+    pi = i
+    pf = i
+    val = copy(i)
+    do while (dabs(val - copy(pf+1)) < thresh2)
+      pf = pf + 1
+      ! if pf == sze, copy(pf+1) will not be valid
+      if (pf == sze) then
+        exit
+      endif
+    enddo
+    ! if pi and pf are different do the average from pi to pf
+    if (pf - pi > 0) then
+      average = 0d0
+      do j = pi, pf
+        average = average + copy(j)
+      enddo
+      average = average / (pf-pi+1)
+      do j = pi, pf
+        copy(j) = average
+      enddo
+      ! Update i
+      i = pf
+    endif
+    ! Update i
+    i = i + 1
+  enddo
 
+  !$OMP PARALLEL &
+  !$OMP SHARED(m,sze,copy_sign,copy,key,A) &
+  !$OMP PRIVATE(i,j,k,idx) &
+  !$OMP DEFAULT(NONE)
+  ! copy -> A
+  !$OMP DO
+  do k = 1, sze
+      idx = key(k)
+      i = mod(idx-1,m) + 1
+      j = (idx-1) / m + 1
+      ! New value with the right sign
+      A(i,j) = sign(copy(k),copy_sign(idx))
+  enddo
+  !$OMP END DO
+  !$OMP END PARALLEL
 
+  deallocate(copy,copy_sign,key)
 
-
+end
-
 
 !subroutine svd_s(A, LDA, U, LDU, D, Vt, LDVt, m, n)
 !  implicit none