ADAS Subroutine xxsort

      subroutine xxsort(n,arr,brr)
      
C-----------------------------------------------------------------------
C
C    ****************** fortran77 subroutine: xxsort ****************** 
C
C  purpose: Sorts array 'arr' into ascending numerical order, with
C           corresponding rearrangement of 'brr'. Uses Shell's method.
C
C  calling program: various
C
C  input        : (i*4) n      = number of array elements
C
C  input/output : (r*8) arr()  = array to be sorted into ascending order
C  input/output : (r*8) brr()  = array corresponding to 'arr'
C
C
C  author: Paul Bryans, University of Strathclyde
C
C  date:   02/12/04
C
C  update: 
C
C-----------------------------------------------------------------------
      INTEGER             N
      REAL*8              ARR(N),      BRR(N)