c----------------------------------------------------------------blocks
        subroutine blocks(nx,ny,nz,np,ne,nop,cord,nxyz,egrp,nbeg,nend,
     *                    nelg,nbb,nee,nelb,nblk,egps,itype,ebox,m,num)
c---------------------------------------------------------------------c
c Purpose:                                                            c
c         To divide FE mesh into blocks.                              c
c---------------------------------------------------------------------c
        common /etype/inode(4)
        integer*2 nop
	dimension nop(20,1),cord(3,1),egrp(6,1),nbeg(1),nend(1),
     *            nelg(1),nee(1),nbb(1),nelb(1),nblk(2,1),egps(6,1),
     *            itype(1),ebox(6,1)
c
        xmax=cord(1,1)
        xmin=cord(1,1)
        ymax=cord(2,1)
        ymin=cord(2,1)
        zmax=cord(3,1)
        zmin=cord(3,1)
        disd=0.0
        do i=1,ne
           if(nop(9,i).eq.0) goto 10
c
c----------store element type
c
           if(nop(20,i).ne.0) then
              itype(i)=3
           else if(nop(15,i).ne.0) then
              itype(i)=2
           else if(nop(13,i).ne.0) then
              itype(i)=4
           else
              itype(i)=1
           endif
c
c----------find B.L. and T.R. conners of each element
c
           ebox(1,i)=cord(1,nop(1,i))
           ebox(4,i)=cord(1,nop(1,i))
           ebox(2,i)=cord(2,nop(1,i))
           ebox(5,i)=cord(2,nop(1,i))
           ebox(3,i)=cord(3,nop(1,i))
           ebox(6,i)=cord(3,nop(1,i))
           do k=2,inode(itype(i))
              ebox(1,i)=min(ebox(1,i),cord(1,nop(k,i)))
              ebox(4,i)=max(ebox(4,i),cord(1,nop(k,i)))
              ebox(2,i)=min(ebox(2,i),cord(2,nop(k,i)))
              ebox(5,i)=max(ebox(5,i),cord(2,nop(k,i)))
              ebox(3,i)=min(ebox(3,i),cord(3,nop(k,i)))
              ebox(6,i)=max(ebox(6,i),cord(3,nop(k,i)))
           enddo
           ebox(1,i)=ebox(1,i)-1.0e-5*abs(ebox(1,i))
           ebox(4,i)=ebox(4,i)+1.0e-5*abs(ebox(4,i))
           ebox(2,i)=ebox(2,i)-1.0e-5*abs(ebox(2,i))
           ebox(5,i)=ebox(5,i)+1.0e-5*abs(ebox(5,i))
           ebox(3,i)=ebox(3,i)-1.0e-5*abs(ebox(3,i))
           ebox(6,i)=ebox(6,i)+1.0e-5*abs(ebox(6,i))
c
c----------calculate the maximum diagonal distance
c
           disd0=sqrt((ebox(4,i)-ebox(1,i))*(ebox(4,i)-ebox(1,i))+
     *                (ebox(5,i)-ebox(2,i))*(ebox(5,i)-ebox(2,i)))
           disd=max(disd,disd0)
c
c-------find B.L. and T.R. conners of the FE mesh
c
           xmax=max(xmax,ebox(4,i))
           xmin=min(xmin,ebox(1,i))
           ymax=max(ymax,ebox(5,i))
           ymin=min(ymin,ebox(2,i))
           zmax=max(zmax,ebox(6,i))
           zmin=min(zmin,ebox(3,i))
   10   enddo

        m=1
        dx=(xmax-xmin)/float(nx)
        if(dx.lt.disd) then
            nx=(xmax-xmin)/disd
            if(nx.lt.1) nx=1
            dx=(xmax-xmin)/float(nx)
        endif
        dy=(ymax-ymin)/float(ny)
        if(dy.lt.disd) then
            ny=(ymax-ymin)/disd
            if(ny.lt.1) ny=1
            dy=(ymax-ymin)/float(ny)
        endif
        dz=(zmax-zmin)/float(nz)
        x=xmin
c
c-------divide into blocks
c
        do i=1,nx
           y=ymin
           do j=1,ny
              z=zmin
              do k=1,nz
                 egrp(1,m)=x-dx*0.01
                 egrp(2,m)=y-dy*0.01
                 egrp(3,m)=z-dz*0.01
                 egrp(4,m)=x+dx*1.01
                 egrp(5,m)=y+dy*1.01
                 egrp(6,m)=z+dz*1.01
                 z=z+dz
                 m=m+1
              enddo
              y=y+dy
           enddo
           x=x+dx
        enddo
        nxyz=nx*ny*nz
        nxyz0=nxyz
        num=1
        do i=1,nxyz
           nbeg(i)=num
           do j=1,ne
              if(nop(9,j).ne.0) then
                 do k=1,inode(itype(j))
                    if(cord(1,nop(k,j)).gt.egrp(4,i).or.
     *                     cord(1,nop(k,j)).lt.egrp(1,i)) goto 30
                    if(cord(2,nop(k,j)).gt.egrp(5,i).or.
     *                     cord(2,nop(k,j)).lt.egrp(2,i)) goto 30
                    if(cord(3,nop(k,j)).gt.egrp(6,i).or.
     *                     cord(3,nop(k,j)).lt.egrp(3,i)) goto 30
                    nelg(num)=j
                    num=num+1
                    goto 40
   30            enddo
              endif
   40      enddo
           nend(i)=num-1
        enddo
        i=1
   45   if(nend(i)-nbeg(i).lt.0) then
           nxyz=nxyz-1
           do j=i,nxyz
              nbeg(j)=nbeg(j+1)
              nend(j)=nend(j+1)
              do k=1,6
                 egrp(k,j)=egrp(k,j+1)
              enddo
           enddo
        else
           i=i+1
        endif
        if(i.le.nxyz) goto 45
c
c-------divide into sub-blocks
c
        m=1
        num=1
        do n=1,nxyz
           num_elem=nend(n)-nbeg(n)+1
           if(num_elem.gt.nxyz+nxyz) then
              a_multiplier=sqrt(float(num_elem))/float(nx*ny)
              nxs=int(nx*a_multiplier)
              if(nxs.lt.1) nxs=1
              nys=int(ny*a_multiplier)
              if(nys.lt.1) nys=1
              dx=(egrp(4,n)-egrp(1,n))/float(nxs)
              dy=(egrp(5,n)-egrp(2,n))/float(nys)
              if(dx.lt.disd) then
                  nxs=(egrp(4,n)-egrp(1,n))/disd
                  if(nxs.lt.1) nxs=1
                  dx=(egrp(4,n)-egrp(1,n))/float(nxs)
              endif
              if(dy.lt.disd) then
                  dy=disd
                  nys=(egrp(5,n)-egrp(2,n))/disd
                  if(nys.lt.1) nys=1
                  dy=(egrp(5,n)-egrp(2,n))/float(nys)
              endif
              nxyzs=nxs*nys
              if(nxyzs.le.1) goto 70
              dz=(egrp(6,n)-egrp(3,n))
           
              nblk(1,n)=nxyzs
              nblk(2,n)=m
              x=egrp(1,n)
              do i=1,nxs
                 y=egrp(2,n)
                 do j=1,nys
                    z=egrp(3,n)
                    egps(1,m)=x-0.01*dx
                    egps(2,m)=y-0.01*dy
                    egps(3,m)=z-0.01*dz
                    egps(4,m)=x+dx*1.01
                    egps(5,m)=y+dy*1.01
                    egps(6,m)=z+dz*1.01
                    y=y+dy
                    m=m+1
                 enddo
                 x=x+dx
              enddo
              do i=nblk(2,n),nblk(2,n)+nblk(1,n)-1
                 nbb(i)=num
                 do j=nbeg(n),nend(n)
                    if(nop(9,nelg(j)).ne.0) then
                       do k=1,inode(itype(nelg(j)))
                          if(cord(1,nop(k,nelg(j))).gt.egps(4,i).or.
     *                     cord(1,nop(k,nelg(j))).lt.egps(1,i)) goto 50
                          if(cord(2,nop(k,nelg(j))).gt.egps(5,i).or.
     *                     cord(2,nop(k,nelg(j))).lt.egps(2,i)) goto 50
                          if(cord(3,nop(k,nelg(j))).gt.egps(6,i).or.
     *                     cord(3,nop(k,nelg(j))).lt.egps(3,i)) goto 50
                          nelb(num)=nelg(j)
                          num=num+1
                          goto 60
   50                  enddo
                    endif
   60            enddo
                 nee(i)=num-1
              enddo
              i=nblk(2,n)
   65         if(nee(i)-nbb(i).lt.0) then
                 nblk(1,n)=nblk(1,n)-1
                 m=m-1
                 do j=i,nblk(2,n)+nblk(1,n)-1
                    nbb(j)=nbb(j+1)
                    nee(j)=nee(j+1)
                    do k=1,6
                       egps(k,j)=egps(k,j+1)
                    enddo
                 enddo
              else
                 i=i+1
              endif
              if(i.le.nblk(2,n)+nblk(1,n)-1) goto 65
           else
   70         nblk(1,n)=1
              nblk(2,n)=m
              nbb(m)=num
              do i=nbeg(n),nend(n)
                 nelb(num)=nelg(i)
                 num=num+1
              enddo
              do j=1,6
                 egps(j,m)=egrp(j,n)
              enddo
              nee(m)=num-1
              m=m+1
           endif
        enddo
        return
        end