Type | Intent | Optional | Attributes | Name | ||
---|---|---|---|---|---|---|

type(davidson_ss), | intent(inout) | :: | this |
|||

integer, | intent(in) | :: | basis_index |

```
subroutine project_hamiltonian_ss(this, basis_index)
type(davidson_ss), intent(inout) :: this
integer, intent(in) :: basis_index
integer :: i
real(dp) :: dot_prod, dot_prod_all
! Multiply the new basis_vector by the hamiltonian and store the result in
! multiplied_basis_vectors.
call multiply_hamil_and_vector_ss(real(this%basis_vectors(:, basis_index), dp), &
this%multiplied_basis_vectors(:, basis_index), this%full_vector, this%sizes, this%displs, this%run)
! Now multiply U^T by (H U) to find projected_hamil. The projected Hamiltonian will
! only differ in the new final column and row. Also, projected_hamil is symmetric.
! Hence, we only need to calculate the final column, and use this to update the final
! row also.
do i = 1, basis_index
if (this%space_size_this_proc > 0) then
dot_prod = dot_product(this%basis_vectors(:, i), this%multiplied_basis_vectors(:, basis_index))
else
dot_prod = 0.0_dp
end if
call MPISumAll(dot_prod, dot_prod_all)
this%projected_hamil(i, basis_index) = dot_prod_all
this%projected_hamil(basis_index, i) = dot_prod_all
end do
! We will use the scrap Hamiltonian to pass into the diagonaliser later, since it
! overwrites this input matrix with the eigenvectors. Hence, make sure the scrap space
! stores the updated projected Hamiltonian.
this%projected_hamil_work = this%projected_hamil
end subroutine project_hamiltonian_ss
```

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