# dppdi.f

          SUBROUTINE DPPDI (AP, N, DET, JOB)
    C***BEGIN PROLOGUE  DPPDI
    C***PURPOSE  Compute the determinant and inverse of a real symmetric
    C            positive definite matrix using factors from DPPCO or DPPFA.
    C***LIBRARY   SLATEC (LINPACK)
    C***CATEGORY  D2B1B, D3B1B
    C***TYPE      DOUBLE PRECISION (SPPDI-S, DPPDI-D, CPPDI-C)
    C***KEYWORDS  DETERMINANT, INVERSE, LINEAR ALGEBRA, LINPACK, MATRIX,
    C             PACKED, POSITIVE DEFINITE
    C***AUTHOR  Moler, C. B., (U. of New Mexico)
    C***DESCRIPTION
    C
    C     DPPDI computes the determinant and inverse
    C     of a double precision symmetric positive definite matrix
    C     using the factors computed by DPPCO or DPPFA .
    C
    C     On Entry
    C
    C        AP      DOUBLE PRECISION (N*(N+1)/2)
    C                the output from DPPCO or DPPFA.
    C
    C        N       INTEGER
    C                the order of the matrix  A .
    C
    C        JOB     INTEGER
    C                = 11   both determinant and inverse.
    C                = 01   inverse only.
    C                = 10   determinant only.
    C
    C     On Return
    C
    C        AP      the upper triangular half of the inverse .
    C                The strict lower triangle is unaltered.
    C
    C        DET     DOUBLE PRECISION(2)
    C                determinant of original matrix if requested.
    C                Otherwise not referenced.
    C                DETERMINANT = DET(1) * 10.0**DET(2)
    C                with  1.0 .LE. DET(1) .LT. 10.0
    C                or  DET(1) .EQ. 0.0 .
    C
    C     Error Condition
    C
    C        A division by zero will occur if the input factor contains
    C        a zero on the diagonal and the inverse is requested.
    C        It will not occur if the subroutines are called correctly
    C        and if DPOCO or DPOFA has set INFO .EQ. 0 .
    C
    C***REFERENCES  J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W.
    C                 Stewart, LINPACK Users' Guide, SIAM, 1979.
    C***ROUTINES CALLED  DAXPY, DSCAL
    C***REVISION HISTORY  (YYMMDD)
    C   780814  DATE WRITTEN
    C   890831  Modified array declarations.  (WRB)
    C   890831  REVISION DATE from Version 3.2
    C   891214  Prologue converted to Version 4.0 format.  (BAB)
    C   900326  Removed duplicate information from DESCRIPTION section.
    C           (WRB)
    C   920501  Reformatted the REFERENCES section.  (WRB)
    C***END PROLOGUE  DPPDI