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NAME
     spbsl - section solve the linear system Ax = b  for  a  sym-
     metric  positive  definite matrix A in banded storage, which
     has been Cholesky-factored by xPBCO or xPBFA, and vectors  b
     and x.

SYNOPSIS
     SUBROUTINE DPBSL (DA, LDA, N, NDIAG, DB)

     SUBROUTINE SPBSL (SA, LDA, N, NDIAG, SB)

     SUBROUTINE ZPBSL (ZA, LDA, N, NDIAG, ZB)

     SUBROUTINE CPBSL (CA, LDA, N, NDIAG, CB)



     #include <sunperf.h>

     void dpbsl(double *abd, int lda, int n, int m, double *b);

     void spbsl(float *abd, int lda, int n, int m, float *b);

     void zpbsl(doublecomplex *abd, int lda, int n, int m,  doub-
               lecomplex *b);

     void cpbsl(complex *abd, int lda, int n, int m, complex *b);

ARGUMENTS
     xA        Cholesky factorization of the matrix  A,  as  com-
               puted by xPBCO or xPBFA.

     LDA       Leading dimension of the array A as specified in a
               dimension or type statement.  LDA >= NDIAG + 1.

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

     NDIAG     Number of diagonals of matrix A.  N-1 >= NDIAG  >=
               0 but if N = 0 then NDIAG = 0.

     xB        On entry, the right-hand side vector b.  On  exit,
               the solution vector x.

SAMPLE PROGRAM
           PROGRAM TEST
           IMPLICIT NONE
     C
           INTEGER           LDA, N, NDIAG
           PARAMETER        (N = 4)
           PARAMETER        (NDIAG = 1)
           PARAMETER        (LDA = NDIAG + 1)
     C
           DOUBLE PRECISION  A(LDA,N), B(N)
           INTEGER           ICOL, INFO, IROW
     C
           EXTERNAL          DPBFA, DPBSL
     C
     C     Initialize the array A to store in banded storage mode
     C     the matrix A shown below.  Initialize the array B to
     C     store the vector B shown below.
     C
     C          2  -1   0   0         60
     C     A = -1   2  -1   0    b = 120
     C          0  -1   2  -1        120
     C          0   0  -1   2         60
     C
           DATA A / 8D8, 2.0D0, -1.0D0, 2.0D0, -1.0D0, 2.0D0, -1.0D0, 2.0D0 /
           DATA B / 6.0D1, 1.2D1, 1.2D1, 6.0D1 /
     C
           PRINT 1000
           PRINT 1010, A(2,1), A(1,2)
           PRINT 1010, A(3,1), A(2,2), A(1,3)
           PRINT 1020,         A(3,2), A(2,3), A(1,4)
           PRINT 1030,                 A(3,3), A(2,4)
           PRINT 1040
           PRINT 1010, ((A(IROW,ICOL), ICOL = 1, N), IROW = 1, LDA)
           PRINT 1050
           PRINT 1060, B
           CALL DPBFA (A, LDA, N, NDIAG, INFO)
           IF (INFO .EQ. 0) THEN
             CALL DPBSL (A, LDA, N, NDIAG, B)
             PRINT 1070
             PRINT 1060, B
           ELSE
             PRINT 1080
           END IF
     C
      1000 FORMAT (1X, 'A in full form:')
      1010 FORMAT (4(3X, F5.1))
      1020 FORMAT (8X, 3(3X, F5.1))
      1030 FORMAT (16X, 3(3X, F5.1))
      1040 FORMAT (/1X, 'A in banded form:  (* in unused entries)')
      1050 FORMAT (/1X, 'b:')
      1060 FORMAT (3X, F5.1)
      1070 FORMAT (/1X, 'A**(-1) * b:')
      1080 FORMAT (/1X, 'A is not positive definite.')
     C
           END

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

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

      b:
         60.0
         12.0
         12.0
         60.0

      A**(-1) * b:
         72.0
         84.0
         84.0
         72.0

Партнёры:

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