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SPOCO(3F)							     SPOCO(3F)


NAME    [Toc]    [Back]

     SPOCO   - SPOCO factors a real symmetric positive definite	matrix and
     estimates the condition of	the matrix.

     If	 RCOND	is not needed, SPOFA is	slightly faster.  To solve  A*X	= B ,
     follow SPOCO by SPOSL.  To	compute	 INVERSE(A)*C ,	follow SPOCO by	SPOSL.
     To	compute	 DETERMINANT(A)	, follow SPOCO by SPODI.  To compute
     INVERSE(A)	, follow SPOCO by SPODI.

SYNOPSYS    [Toc]    [Back]

      SUBROUTINE SPOCO(A,LDA,N,RCOND,Z,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 an upper	triangular matrix  R  so that  A = TRANS(R)*R
	where  TRANS(R)	 is the	transpose.
	The strict lower triangle is unaltered.
	If  INFO .NE. 0	, the factorization is not complete.

     RCOND REAL
	an estimate of the reciprocal condition	of  A .
	For the	system	A*X = B	, relative perturbations
	in  A  and  B  of size	EPSILON	 may cause
	relative perturbations in  X  of size  EPSILON/RCOND .
	If  RCOND  is so small that the	logical	expression
	1.0 + RCOND .EQ. 1.0
	is true, then  A  may be singular to working
	precision.  In particular,  RCOND  is zero  if
	exact singularity is detected or the estimate
	underflows.  If	INFO .NE. 0 , RCOND is unchanged.

     Z REAL(N)
	a work vector whose contents are usually unimportant.
	If  A  is close	to a singular matrix, then  Z  is
	an approximate null vector in the sense	that
	NORM(A*Z) = RCOND*NORM(A)*NORM(Z) .
	If  INFO .NE. 0	, Z  is	unchanged.

     INFO INTEGER
	= 0  for normal	return.



									Page 1






SPOCO(3F)							     SPOCO(3F)



	= K  signals an	error condition.  The leading minor
	of order  K  is	not positive definite.	LINPACK.  This version dated
     08/14/78 .	 Cleve Moler, University of New	Mexico,	Argonne	National Lab.
     Subroutines and Functions LINPACK SPOFA BLAS SAXPY,SDOT,SSCAL,SASUM
     Fortran ABS,AMAX1,REAL,SIGN


									PPPPaaaaggggeeee 2222
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