SSIDI(3F)							     SSIDI(3F)

NAME    [Toc]    [Back]

     SSIDI   - SSIDI computes the determinant, inertia and inverse of a	real
     symmetric matrix using the	factors	from SSIFA.

SYNOPSYS    [Toc]    [Back]

      SUBROUTINE SSIDI(A,LDA,N,KPVT,DET,INERT,WORK,JOB)

DESCRIPTION    [Toc]    [Back]

     On	Entry

     A REAL(LDA,N)
	the output from	SSIFA.

     LDA INTEGER
	the leading dimension of the array A.

     N INTEGER
	the order of the matrix	A.

     KPVT INTEGER(N)
	the pivot vector from SSIFA.

     WORK REAL(N)
	work vector.  Contents destroyed.

     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.

     A contains	the upper triangle of the inverse of
	the original matrix.  The strict lower triangle
	is never referenced.

     DET REAL(2)
	determinant of original	matrix.
	Determinant = DET(1) * 10.0**DET(2)
	with 1.0 .LE. ABS(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	may occur if the inverse is requested and  SSICO  has
     set RCOND .EQ. 0.0	or  SSIFA  has set  INFO .NE. 0	.  LINPACK.  This



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SSIDI(3F)							     SSIDI(3F)



     version dated 08/14/78 .  James Bunch, Univ. Calif. San Diego, Argonne
     Nat. Lab Subroutines and Functions	BLAS SAXPY,SCOPY,SDOT,SSWAP Fortran
     ABS,IABS,MOD


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