eveqnuv.f90

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! Copyright (C) 2019 Chung-Yu Wang, J. K. Dewhurst, S. Sharma and
! E. K. U. Gross. This file is distributed under the terms of the GNU General
! Public License. See the file COPYING for license details.

subroutine eveqnuv(n,au,bv,w)
implicit none
! arguments
integer, intent(in) :: n
complex(8), intent(inout) :: au(n,n),bv(n,n)
real(8), intent(out) :: w(n)
! local variables
integer n2,i,j
! allocatable arrays
real(8), allocatable :: w2(:)
complex(8), allocatable :: h(:,:)
n2=2*n
! setup the fermionic Bogoliubov Hamiltonian
allocate(w2(n2),h(n2,n2))
do j=1,n
  do i=1,j
    h(i,j)=au(i,j)
    h(n+i,n+j)=-au(i,j)
  end do
end do
do j=1,n
  do i=1,n
    h(i,n+j)=bv(i,j)
  end do
end do
! find the eigenvalues and eigenvectors
call zheevdi(n2,n2,h,w2)
! copy to output arrays
do i=1,n
! choose the positive eigenvalues
  j=n+i
  w(i)=w2(j)
  au(1:n,i)=h(1:n,j)
  bv(1:n,i)=h(n+1:n2,j)
end do
deallocate(w2,h)
end subroutine