DLAMRG will create a permutation list which will merge the elements
 of A (which is composed of two independently sorted sets) into a
 single set which is sorted in ascending order.

          N1 is INTEGER

          N2 is INTEGER
         These arguements contain the respective lengths of the two
         sorted lists to be merged.

          A is DOUBLE PRECISION array, dimension (N1+N2)
         The first N1 elements of A contain a list of numbers which
         are sorted in either ascending or descending order.  Likewise
         for the final N2 elements.

          DTRD1 is INTEGER

          DTRD2 is INTEGER
         These are the strides to be taken through the array A.
         Allowable strides are 1 and -1.  They indicate whether a
         subset of A is sorted in ascending (DTRDx = 1) or descending
         (DTRDx = -1) order.

          INDEX is INTEGER array, dimension (N1+N2)
         On exit this array will contain a permutation such that
         if B( I ) = A( INDEX( I ) ) for I=1,N1+N2, then B will be
         sorted in ascending order.