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NAME
     sppfa - compute a  Cholesky  factorization  of  a  symmetric
     positive definite matrix A in packed storage.  It is typical
     to follow a call to xPPFA with a call to xPPSL to solve Ax =
     b or to xPPDI to compute the determinant and inverse of A.

SYNOPSIS
     SUBROUTINE DPPFA (DA, N, INFO)

     SUBROUTINE SPPFA (SA, N, INFO)

     SUBROUTINE ZPPFA (ZA, N, INFO)

     SUBROUTINE CPPFA (CA, N, INFO)



     #include <sunperf.h>

     void dppfa(double *dap, int n, int *info) ;

     void sppfa(float *sap, int n, int *info) ;

     void zppfa(doublecomplex *zap, int n, int *info) ;

     void cppfa(complex *cap, int n, int *info) ;

ARGUMENTS
     xA        On entry, the upper triangle of the matrix A.   On
               exit, a Cholesky factorization of the matrix A.

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

     INFO      On exit:
               INFO = 0  Subroutine completed normally.
               INFO > 0  Returns a value k if U(k,k) = 0 to indi-
               cate that xGESL will divide by zero if called.

SAMPLE PROGRAM
           PROGRAM TEST
           IMPLICIT NONE
     C
           INTEGER           LENGTA, N
           PARAMETER        (N = 4)
           PARAMETER        (LENGTA = (N * N + N) / 2)
     C
           DOUBLE PRECISION  A(LENGTA), B(N)
           INTEGER           INFO
     C
           EXTERNAL          DPPFA, DPPSL
     C
     C     Initialize the array A to store in packed symmetric storage
     C     mode the matrix A shown below.  Initialize the array B to store
     C     the vector B shown below.
     C
     C         4  3  2  1        30
     C     A = 3  4  3  2    b = 20
     C         2  3  4  3        20
     C         1  2  3  4        40
     C
           DATA A / 4.0D0, 3.0D0, 4.0D0, 2.0D0, 3.0D0, 4.0D0,
          $         1.0D0, 2.0D0, 3.0D0, 4.0D0 /
           DATA B / 6.0D1, 2.0D1, 2.0D1, 6.0D1 /
     C
           PRINT 1000
           PRINT 1010, A(1), A(2), A(4), A(7)
           PRINT 1010, A(2), A(3), A(5), A(8)
           PRINT 1010, A(4), A(5), A(6), A(9)
           PRINT 1010, A(7), A(8), A(9), A(10)
           PRINT 1020
           PRINT 1030, B
           CALL DPPFA (A, N, INFO)
           IF (INFO .EQ. 0) THEN
             CALL DPPSL (A, N, B)
             PRINT 1040
             PRINT 1030, B
           ELSE
             PRINT 1050
           END IF
     C
      1000 FORMAT (1X, 'A in full form:')
      1010 FORMAT (5(3X, F5.1))
      1020 FORMAT (/1X, 'b:')
      1030 FORMAT (3X, F5.1)
      1040 FORMAT (/1X, 'A**(-1) * b:')
      1050 FORMAT (/1X, 'A is too ill-conditioned.')
     C
           END

SAMPLE OUTPUT
      A in full form:
          4.0     3.0     2.0     1.0
          3.0     4.0     3.0     2.0
          2.0     3.0     4.0     3.0
          1.0     2.0     3.0     4.0

      b:
         60.0
         20.0
         20.0
         60.0

      A**(-1) * b:
         32.0

        -20.0
        -20.0
         32.0

Партнёры:

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