SSIFA(3F)							     SSIFA(3F)

NAME    [Toc]    [Back]

     SSIFA   - SSIFA factors a real symmetric matrix by	elimination with
     symmetric pivoting.

     To	solve  A*X = B , follow	SSIFA by SSISL.	 To compute  INVERSE(A)*C ,
     follow SSIFA by SSISL.  To	compute	 DETERMINANT(A)	, follow SSIFA by
     SSIDI.  To	compute	 INERTIA(A) , follow SSIFA by SSIDI.  To compute
     INVERSE(A)	, follow SSIFA by SSIDI.

SYNOPSYS    [Toc]    [Back]

      SUBROUTINE SSIFA(A,LDA,N,KPVT,INFO)

DESCRIPTION    [Toc]    [Back]

     On	Entry

     A REAL(LDA,N)
	the symmetric matrix to	be factored.
	Only the diagonal and upper triangle are used.

     LDA INTEGER
	the leading dimension of the array  A .

     N INTEGER
	the order of the matrix	 A .  On Return

     A a block diagonal	matrix and the multipliers which
	were used to obtain it.
	The factorization can be written  A = U*D*TRANS(U)
	where  U  is a product of permutation and unit
	upper triangular matrices , TRANS(U) is	the
	transpose of  U	, and  D  is block diagonal
	with 1 by 1 and	2 by 2 blocks.

     KPVT INTEGER(N)
	an integer vector of pivot indices.

     INFO INTEGER
	= 0  normal value.
	= K  if	the K-th pivot block is	singular.  This	is
	not an error condition for this	subroutine,
	but it does indicate that SSISL	or SSIDI may
	divide by zero if called.  LINPACK.  This version dated	08/14/78 .
     James Bunch, Univ.	Calif. San Diego, Argonne Nat. Lab.  Subroutines and
     Functions BLAS SAXPY,SSWAP,ISAMAX Fortran ABS,AMAX1,SQRT


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