Sorts a real array by nondecreasing absolute value and return the permutation that rearranges the array.

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.

IPERM — Vector of length N.   (Input/Output)
On input, IPERM should be initialized to the values 1, 2, …, N. On output, IPERM contains a record of permutations made on the vector IA.

Optional Arguments

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

FORTRAN 90 Interface

Generic:                              CALL SVRBP (RA, RB, IPERM [,…])

Specific:                             The specific interface names are S_SVRBP and D_SVRBP.

FORTRAN 77 Interface

Single:                                CALL SVRBP (N, RA, RB, IPERM)

Double:                              The double precision name is DSVRBP.

Description

Routine SVRBP sorts the elements of an array, A, into ascending order by absolute value, keeping a record in P of the permutations to the array A. That is, the elements of P are moved in the same manner as are the elements in A as A is being sorted. The routine SVRBP uses the algorithm discussed in SVRGN. On completion, Aj ≤ Ai for j < i.

Comments

For wider applicability, integers (1, 2, …, N) that are to be associated with RA(I) for I = 1, 2, …, N may be entered into IPERM(I) in any order. Note that these integers must be unique.

Example

This example sorts the 10-element array RA by absolute value.

 

      USE SVRBP_INT

      USE UMACH_INT

 

      IMPLICIT   NONE

!                                 Declare variables

      INTEGER N, J, NOUT, I

      PARAMETER  (N=10)

      REAL       RA(N), RB(N)

      INTEGER    IPERM(N)

!                                 Set values for  RA and IPERM

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

!

!    IPERM = ( 1  2  3  4  5  6  7  8  9  10 )

!

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

      DATA IPERM/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/

!                                 Sort RA by absolute value into RB

      CALL SVRBP (RA, RB, IPERM)

!                                 Print results

      CALL UMACH (2,NOUT)

      WRITE (NOUT, 99998) (RB(J),J=1,N)

      WRITE (NOUT, 99999) (IPERM(I),I=1,N)

!

99998 FORMAT ('  The output vector is:', /, 10(1X,F5.1))

99999 FORMAT ('  The permutation vector is:', /, 10(1X,I5))

      END

Output

 

The output vector is:
1.0  -2.0   3.0  -4.0   5.0   6.0   7.0   8.0   9.0  10.0
The permutation vector is:
10     9     8     7     6     5     4     3     2     1

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