DSPDI(3F)							     DSPDI(3F)

NAME    [Toc]    [Back]

     DSPDI   - DSPDI computes the determinant, inertia and inverse of a	double
     precision symmetric matrix	using the factors from DSPFA, where the	matrix
     is	stored in packed form.

SYNOPSYS    [Toc]    [Back]

      SUBROUTINE DSPDI(AP,N,KPVT,DET,INERT,WORK,JOB)

DESCRIPTION    [Toc]    [Back]

     On	Entry

     AP	DOUBLE PRECISION (N*(N+1)/2)
	the output from	DSPFA.

     N INTEGER
	the order of the matrix	A.

     KPVT INTEGER(N)
	the pivot vector from DSPFA.

     WORK DOUBLE PRECISION(N)
	work vector.  Contents ignored.

     JOB INTEGER
	JOB has	the decimal expansion  ABC  where
	if  C .NE. 0, the inverse is computed,
	if  B .NE. 0, the determinant is computed,
	if  A .NE. 0, the inertia is computed.
	For example, JOB = 111	gives all three.  On Return Variables not
     requested by JOB are not used.

     AP	contains the upper triangle of the inverse of
	the original matrix, stored in packed form.
	The columns of the upper triangle are stored
	sequentially in	a one-dimensional array.

     DET DOUBLE	PRECISION(2)
	determinant of original	matrix.
	DETERMINANT = DET(1) * 10.0**DET(2)
	with 1.0 .LE. DABS(DET(1)) .LT.	10.0
	or DET(1) = 0.0.

     INERT INTEGER(3)
	the inertia of the original matrix.
	INERT(1)  =  number of positive	eigenvalues.
	INERT(2)  =  number of negative	eigenvalues.
	INERT(3)  =  number of zero eigenvalues.  Error	Condition

     A division	by zero	will occur if the inverse is requested and  DSPCO  has
     set RCOND .EQ. 0.0	or  DSPFA  has set  INFO .NE. 0	.  LINPACK.  This
     version dated 08/14/78 .  James Bunch, Univ. Calif. San Diego, Argonne



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DSPDI(3F)							     DSPDI(3F)



     Nat. Lab.	Subroutines and	Functions BLAS DAXPY,DCOPY,DDOT,DSWAP Fortran
     DABS,IABS,MOD


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