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NAME
     dgbco - compute the LU factorization and condition number of
     a  general  matrix  A  in  banded storage.  If the condition
     number is not needed then xGBFA is slightly faster.   It  is
     typical  to  follow  a call to xGBCO with a call to xGBSL to
     solve Ax = b or to xGBDI to compute the determinant of A.

SYNOPSIS
     SUBROUTINE DGBCO (DA, LDA, N, NSUB, NSUPER, IPIVOT,  DRCOND,
               DWORK)

     SUBROUTINE SGBCO (SA, LDA, N, NSUB, NSUPER, IPIVOT,  SRCOND,
               SWORK)

     SUBROUTINE ZGBCO (ZA, LDA, N, NSUB, NSUPER, IPIVOT,  DRCOND,
               ZWORK)

     SUBROUTINE CGBCO (CA, LDA, N, NSUB, NSUPER, IPIVOT,  SRCOND,
               CWORK)



     #include <sunperf.h>

     void dgbco(double *abd, int lda, int n, int ml, int mu,  int
               *ipivot, double *rcond) ;

     void sgbco(float *abd, int lda, int n, int ml, int  mu,  int
               *ipivot, float *rcond) ;

     void zgbco(doublecomplex *abd, int lda, int n, int  ml,  int
               mu, int *ipivot, double *rcond) ;

     void cgbco(complex *abd, int lda, int n, int ml, int mu, int
               *ipivot, float *rcond) ;

ARGUMENTS
     xA        On entry, the matrix A.  On exit, an LU factoriza-
               tion of the matrix A.

     LDA       Leading dimension of the array A as specified in a
               dimension or type statement.

     LDA       * 2 * NSUB + NSUPER + 1.

     N         Order of the matrix A.  N >= 0.

     NSUB      Number of subdiagonals of A.  N-1 >= NSUB >= 0 but
               if N = 0 then NSUB = 0.

     NSUPER    Number of superdiagonals of A.  N-1 >= NSUPER >= 0
               but if N = 0 then NSUPER = 0.

     IPIVOT    On exit, a vector of pivot indices.

     xRCOND    On exit, an estimate of the  reciprocal  condition
               number  of  A.  0.0 <= RCOND <= 1.0.  As the value
               of RCOND gets smaller, operations with A  such  as
               solving  Ax  =  b may become less stable. If RCOND
               satisfies RCOND + 1.0 = 1.0 then A may be singular
               to working precision.

     xWORK     Scratch array with a dimension of N.

SAMPLE PROGRAM
           PROGRAM TEST
           IMPLICIT NONE
     C
           INTEGER           IAXEQB, LDA, LDAB, N, NDIAG, NSUB, NSUPER
           PARAMETER        (IAXEQB = 0)
           PARAMETER        (N = 4)
           PARAMETER        (LDA = N)
           PARAMETER        (NSUB = 1)
           PARAMETER        (NSUPER = 1)
           PARAMETER        (NDIAG = NSUB + 1 + NSUPER)
           PARAMETER        (LDAB = 2 * NSUB + 1 + NSUPER)
     C
           DOUBLE PRECISION  AB(LDAB,N), AG(LDA,N), B(N), RCOND, WORK(N)
           INTEGER           ICOL, IPIVOT(N), IROW, IROWB, I1, I2, JOB
     C
           EXTERNAL          DGBCO, DGBSL
           INTRINSIC         MAX0, MIN0
     C
     C     Initialize the array AG to store the 4x4 matrix A with one
     C     subdiagonal and one superdiagonal shown below.  Initialize
     C     the array B to store the vector b shown below.
     C
     C           2  -1                5
     C     AG = -1   2  -1        b = 5
     C              -1   2  -1        5
     C                  -1   2        5
     C
           DATA AB / 16*8D8 /
           DATA AG /  2.0D0, -1.0D0,  2*0D0, -1.0D0,  2.0D0, -1.0D0,
          $           2*0D0, -1.0D0,  2.0D0, -1.0D0,  2*0D0, -1.0D0,
          $           2.0D0 /
           DATA B / N*5.0D0 /
     C
     C     Copy the matrix A from the array AG to the array AB.  The
     C     matrix is stored in general storage mode in AG and it will
     C     be stored in banded storage mode in AB.  The code to copy
     C     from general to banded storage mode is taken from the
     C     comment block in the original DGBFA by Cleve Moler.
     C
           DO 10, ICOL = 1, N
             I1 = MAX0 (1, ICOL - NSUPER)
             I2 = MIN0 (N, ICOL + NSUB)
             DO 10, IROW = I1, I2
               IROWB = IROW - ICOL + NDIAG
               AB(IROWB,ICOL) = AG(IROW,ICOL)
        10   CONTINUE
        20 CONTINUE
     C
     C     Print the initial values of the arrays.
     C
           PRINT 1000
           PRINT 1010, ((AG(IROW,ICOL), ICOL = 1, N), IROW = 1, N)
           PRINT 1020
           PRINT 1010, ((AB(IROW,ICOL), ICOL = 1, N),
          $             IROW = 2 * NSUB, 2 * NSUB + 1 + NSUPER)
           PRINT 1030
           PRINT 1040, B
     C
     C     Factor the matrix in banded form.
     C
           CALL DGBCO (AB, LDA, N, NSUB, NSUPER, IPIVOT, RCOND, WORK)
           PRINT 1050, RCOND
           IF ((RCOND + 1.0D0) .EQ. 1.0D0) THEN
             PRINT 1070
           END IF
           JOB = IAXEQB
           CALL DGBSL (AB, LDA, N, NSUB, NSUPER, IPIVOT, B, JOB)
           PRINT 1060
           PRINT 1040, B
     C
      1000 FORMAT (1X, 'A in full form:')
      1010 FORMAT (4(3X, F4.1))
      1020 FORMAT (/1X, 'A in banded form:  (* in unused elements)')
      1030 FORMAT (/1X, 'b:')
      1040 FORMAT (3X, F4.1)
      1050 FORMAT (/1X, 'Reciprocal of the condition number: ', F5.2)
      1060 FORMAT (/1X, 'A**(-1) * b:')
      1070 FORMAT (1X, 'A may be singular to working precision.')
     C
           END

SAMPLE OUTPUT
      A in full form:
         2.0   -1.0    0.0    0.0
        -1.0    2.0   -1.0    0.0
         0.0   -1.0    2.0   -1.0
         0.0    0.0   -1.0    2.0

      A in banded form:  (* in unused elements)
        ****   -1.0   -1.0   -1.0
         2.0    2.0    2.0    2.0
        -1.0   -1.0   -1.0   ****

      b:
         5.0
         5.0
         5.0
         5.0

      Reciprocal of the condition number:  0.08

      A**(-1) * b:
        10.0
        15.0
        15.0
        10.0

Партнёры:

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