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NAME
     sptsl - solve the linear system Ax = b for a symmetric posi-
     tive definite tridiagonal matrix A and vectors b and x.

SYNOPSIS
     SUBROUTINE DPTSL (N, DDIAG, DOFFD, DB)

     SUBROUTINE SPTSL (N, SDIAG, SOFFD, SB)

     SUBROUTINE ZPTSL (N, ZDIAG, ZOFFD, ZB)

     SUBROUTINE CPTSL (N, CDIAG, COFFD, CB)



     #include <sunperf.h>

     void dptsl(int n, double *d, double *e, double *b) ;

     void sptsl(int n, float *d, float *e, float *b) ;

     void zptsl(int n, doublecomplex *d, doublecomplex *e,  doub-
               lecomplex *b) ;

     void cptsl(int n, complex *d, complex *e, complex *b) ;

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

     xDIAG     Main diagonal elements of A.

     xOFFD     Off  diagonal  elements  of  A.   OFFD(1)  through
               OFFD(N*1)  contains  the  off  diagonal  elements;
               OFFD(N) is not referenced.

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

SAMPLE PROGRAM
           PROGRAM TEST
           IMPLICIT NONE
     C
           INTEGER           N
           PARAMETER        (N = 4)
     C
           DOUBLE PRECISION  B(N), SUBD(N), DIAG(N)
     C
           EXTERNAL          DPTSL
     C
     C     Initialize the arrays SUBD and DIAG to store the subdiagonal
     C     and diagonal of the tridiagonal positive definite matrix A
     C     shown below.  Initialize the array B to store the right hand
     C     side vector b shown below.
     C
     C          2  -1                 6
     C     A = -1   2  -1        b = 12
     C             -1   2  -1        12
     C                 -1   2         6
     C
           DATA SUBD / -1.0D0, -1.0D0, -1.0D0, 8D8 /
           DATA DIAG / 4*2.0D0 /
           DATA B / 6.0D0, 1.2D1, 1.2D1, 6.0D0 /
     C
           PRINT 1000
           PRINT 1010, DIAG(1), SUBD(1)
           PRINT 1020, SUBD(1), DIAG(2), SUBD(2)
           PRINT 1030,          SUBD(2), DIAG(3), SUBD(3)
           PRINT 1040,                   SUBD(3), DIAG(4)
           PRINT 1050
           PRINT 1060, B
           CALL DPTSL (N, DIAG, SUBD, B)
           PRINT 1070
           PRINT 1060, B
     C
      1000 FORMAT (1X, 'A:')
      1010 FORMAT (1X, 2(2X, F4.1))
      1020 FORMAT (1X, 3(2X, F4.1))
      1030 FORMAT (1X,  6X, 3(2X, F4.1))
      1040 FORMAT (1X, 12X, 2(2X, F4.1))
      1050 FORMAT (/1X, 'b:')
      1060 FORMAT (3X, F6.1)
      1070 FORMAT (/1X, 'A**(-1) * b:')
     C
           END

SAMPLE OUTPUT
      A:
         2.0  -1.0
        -1.0   2.0  -1.0
              -1.0   2.0  -1.0
                    -1.0   2.0

      b:
           6.0
          12.0
          12.0
           6.0

      A**(-1) * b:
          18.0
          30.0
          30.0
          18.0

Партнёры:

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