1 files changed, 63 insertions, 0 deletions
diff --git a/neighbourList.f90 b/neighbourList.f90
new file mode 100644
index 0000000..8bf9c14
--- /dev/null
+++ b/neighbourList.f90
@@ -0,0 +1,63 @@
+subroutine ONETO2(id, x, y)
+    implicit none
+    integer, intent(in)  :: id
+    integer, intent(out) :: x, y
+
+    y = id / b
+    x = mod(id, b)
+end subroutine ONETO2
+
+function TWOtoONE(x, y) result(id)
+    implicit none
+    integer, intent(in) :: x, y
+    integer :: id
+
+    id = y * b + x
+end function TWOtoONE
+
+function get_neighbour_ids(p) result (neighbours)
+    integer, intent(in) :: p !> The sequential position
+    integer, allocatable, dimension(:) :: neighbours !> The list of neighbours
+    integer :: i,j,k
+    integer :: x_cell, y_cell, x_test, y_test
+    integer :: max_list(9)
+
+    !> Don't save the values between calls
+    k = 1
+    max_list = -1
+
+    call ONETO2(p,x_cell,y_cell)
+    max_list(k) = p
+
+    !print *, max_list
+
+    !> Start by just getting all of the neighbours
+    do i = -1,1
+        do j = -1,1
+            if(i == 0 .and. j == 0) cycle !> Skip the cell itself
+            
+            !> The "test" coordinate
+            x_test = x_cell + i
+            y_test = y_cell + j
+
+            !> If the coordinates are real (within the expected range), add them to the list:
+            if((x_test .ge. 0 .and. x_test .lt. b) .and. (y_test .ge. 0 .and. y_test .lt. b)) then
+                !> Increment the number of correct coordinates
+                k = k + 1
+                !> Flip a zero to the new coordinate in the max list
+                max_list(k) = TWOtoONE(x_test, y_test)
+            end if
+        end do
+    end do
+
+    !> Return a vector of all non-zero elements
+!    neighbours = pack(max_list, max_list>= 0.0)
+    neighbours = max_list ! entries -1 must be skipped as they correspond to non-existent neighbours at the edge or corner
+end function get_neighbour_ids
+    
+subroutine buildNBL()
+  integer :: sector
+  do sector=0,b*b-1
+     nbl(sector,:) = get_neighbour_ids(sector)
+  end do
+end subroutine buildNBL