DSIFA(3F)							     DSIFA(3F)

NAME    [Toc]    [Back]

     DSIFA   - DSIFA factors a double precision	symmetric matrix by
     elimination with symmetric	pivoting.

     To	solve  A*X = B , follow	DSIFA by DSISL.	 To compute  INVERSE(A)*C ,
     follow DSIFA by DSISL.  To	compute	 DETERMINANT(A)	, follow DSIFA by
     DSIDI.  To	compute	 INERTIA(A) , follow DSIFA by DSIDI.  To compute
     INVERSE(A)	, follow DSIFA by DSIDI.

SYNOPSYS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     On	Entry

     A DOUBLE PRECISION(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 DSISL	or DSIDI 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 DAXPY,DSWAP,IDAMAX Fortran DABS,DMAX1,DSQRT


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