[Pw_forum] complex band

[Manoj Srivastava]

Dear Alexander, PWSCF users and developers, 
 I have a technical question in one of the subroutines used to calculate
complex band. The subroutine 'init_gper.f90' under PWCOND directory is
used to calculate number of G perpendicular vectors within the energy
cutoff by using [k_{\perp}+G_{\perp}]^2.le.E_{cut}. I understand the
counting of Gper, but i dont understand how do they construct the Gper
vectors. For example what is 'ngpsh'? It is defined as 'no. of shells for
G', but i really dont understand what this is. I dont understand after
line 50 of the code in init_gper.f90.  Mainly what does the following
piece of code do
         
          do i=1,nrx
	  do j=1,nry
           icount=0
          do iw=1, ngpsh
           if (abs(norm2-gnorm2(iw)).gt.eps) then
             icount=icount+1
           else
             nshell(i,j)=iw
           endif
         enddo
         if (icount.eq.ngpsh) then
           ngpsh=ngpsh+1
           gnorm2(ngpsh)=norm2
           nshell(i,j)=ngpsh
         endif
      endif
      enddo
      enddo
I understand it is not a good way of asking question, but I am completely
lost. Any help will be appreciated. 

Regards, 
Manoj