DTRCO(3F)							     DTRCO(3F)

NAME    [Toc]    [Back]

     DTRCO   - DTRCO estimates the condition of	a double precision triangular
     matrix.

SYNOPSYS    [Toc]    [Back]

      SUBROUTINE DTRCO(T,LDT,N,RCOND,Z,JOB)

DESCRIPTION    [Toc]    [Back]

     On	Entry

     T DOUBLE PRECISION(LDT,N)
	T contains the triangular matrix.  The zero
	elements of the	matrix are not referenced, and
	the corresponding elements of the array	can be
	used to	store other information.

     LDT INTEGER
	LDT is the leading dimension of	the array T.

     N INTEGER
	N is the order of the system.

     JOB INTEGER
	= 0	    T  is lower	triangular.
	= nonzero   T  is upper	triangular.  On	Return

     RCOND DOUBLE PRECISION
	an estimate of the reciprocal condition	of  T .
	For the	system	T*X = B	, relative perturbations
	in  T  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  T  may be singular to working
	precision.  In particular,  RCOND  is zero  if
	exact singularity is detected or the estimate
	underflows.

     Z DOUBLE PRECISION(N)
	a work vector whose contents are usually unimportant.
	If  T  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) .  LINPACK.  This version dated
     08/14/78 .	 Cleve Moler, University of New	Mexico,	Argonne	National Lab.
     Subroutines and Functions BLAS DAXPY,DSCAL,DASUM Fortran DABS,DMAX1,DSIGN


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