Sorts a real array by algebraically increasing value.

Required Arguments

RA — Vector of length N containing the array to be sorted.   (Input)

RB — Vector of length N containing the sorted array.   (Output)
If RA is not needed, RA and RB can share the same storage locations.

Optional Arguments

N — Number of elements in the array to be sorted.   (Input)
Default: N = size (RA,1).

FORTRAN 90 Interface

Generic:                              CALL SVRGN (RA, RB [,…])

Specific:                             The specific interface names are S_SVRGN and D_SVRGN.

FORTRAN 77 Interface

Single:                                CALL SVRGN (N, RA, RB)

Double:                              The double precision name is DSVRGN.

Description

Routine SVRGN sorts the elements of an array, A, into ascending order by algebraic value. The array A is divided into two parts by picking a central element T of the array. The first and last elements of A are compared with T and exchanged until the three values appear in the array in ascending order. The elements of the array are rearranged until all elements greater than or equal to the central element appear in the second part of the array and all those less than or equal to the central element appear in the first part. The upper and lower subscripts of one of the segments are saved, and the process continues iteratively on the other segment. When one segment is finally sorted, the process begins again by retrieving the subscripts of another unsorted portion of the array. On completion, Aj ≤ Ai for j < i. For more details, see Singleton (1969), Griffin and Redish (1970), and Petro (1970).

Example

This example sorts the 10-element array RA algebraically.

 

      USE SVRGN_INT

      USE UMACH_INT

 

      IMPLICIT   NONE

!                                 Declare variables

      INTEGER    N, NOUT, J

      PARAMETER  (N=10)

      REAL       RA(N), RB(N)

!                                 Set values for  RA

!     RA = ( -1.0  2.0  -3.0  4.0  -5.0  6.0  -7.0  8.0  -9.0  10.0 )

!

      DATA RA/-1.0, 2.0, -3.0, 4.0, -5.0, 6.0, -7.0, 8.0, -9.0, 10.0/

!                                 Sort RA by algebraic value into RB

      CALL SVRGN (RA, RB)

!                                 Print results

      CALL UMACH (2,NOUT)

      WRITE (NOUT, 99999) (RB(J),J=1,N)

!

99999 FORMAT ('  The output vector is:', /, 10(1X,F5.1))

      END

Output

 

The Output vector is:
-9.0  -7.0  -5.0  -3.0  -1.0   2.0   4.0   6.0   8.0  10.0

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