dlatdf.f(3)							      LAPACK							       dlatdf.f(3)

NAME

       dlatdf.f -

SYNOPSIS

   Functions/Subroutines
       subroutine dlatdf (IJOB, N, Z, LDZ, RHS, RDSUM, RDSCAL, IPIV, JPIV)
	   DLATDF uses the LU factorization of the n-by-n matrix computed by sgetc2 and computes a contribution to the reciprocal Dif-estimate.

Function/Subroutine Documentation
   subroutine dlatdf (integerIJOB, integerN, double precision, dimension( ldz, * )Z, integerLDZ, double precision, dimension( * )RHS, double
       precisionRDSUM, double precisionRDSCAL, integer, dimension( * )IPIV, integer, dimension( * )JPIV)
       DLATDF uses the LU factorization of the n-by-n matrix computed by sgetc2 and computes a contribution to the reciprocal Dif-estimate.

       Purpose:

	    DLATDF uses the LU factorization of the n-by-n matrix Z computed by
	    DGETC2 and computes a contribution to the reciprocal Dif-estimate
	    by solving Z * x = b for x, and choosing the r.h.s. b such that
	    the norm of x is as large as possible. On entry RHS = b holds the
	    contribution from earlier solved sub-systems, and on return RHS = x.

	    The factorization of Z returned by DGETC2 has the form Z = P*L*U*Q,
	    where P and Q are permutation matrices. L is lower triangular with
	    unit diagonal elements and U is upper triangular.

       Parameters:
	   IJOB

		     IJOB is INTEGER
		     IJOB = 2: First compute an approximative null-vector e
			 of Z using DGECON, e is normalized and solve for
			 Zx = +-e - f with the sign giving the greater value
			 of 2-norm(x). About 5 times as expensive as Default.
		     IJOB .ne. 2: Local look ahead strategy where all entries of
			 the r.h.s. b is choosen as either +1 or -1 (Default).

	   N

		     N is INTEGER
		     The number of columns of the matrix Z.

	   Z

		     Z is DOUBLE PRECISION array, dimension (LDZ, N)
		     On entry, the LU part of the factorization of the n-by-n
		     matrix Z computed by DGETC2:  Z = P * L * U * Q

	   LDZ

		     LDZ is INTEGER
		     The leading dimension of the array Z.  LDA >= max(1, N).

	   RHS

		     RHS is DOUBLE PRECISION array, dimension (N)
		     On entry, RHS contains contributions from other subsystems.
		     On exit, RHS contains the solution of the subsystem with
		     entries acoording to the value of IJOB (see above).

	   RDSUM

		     RDSUM is DOUBLE PRECISION
		     On entry, the sum of squares of computed contributions to
		     the Dif-estimate under computation by DTGSYL, where the
		     scaling factor RDSCAL (see below) has been factored out.
		     On exit, the corresponding sum of squares updated with the
		     contributions from the current sub-system.
		     If TRANS = 'T' RDSUM is not touched.
		     NOTE: RDSUM only makes sense when DTGSY2 is called by STGSYL.

	   RDSCAL

		     RDSCAL is DOUBLE PRECISION
		     On entry, scaling factor used to prevent overflow in RDSUM.
		     On exit, RDSCAL is updated w.r.t. the current contributions
		     in RDSUM.
		     If TRANS = 'T', RDSCAL is not touched.
		     NOTE: RDSCAL only makes sense when DTGSY2 is called by
			   DTGSYL.

	   IPIV

		     IPIV is INTEGER array, dimension (N).
		     The pivot indices; for 1 <= i <= N, row i of the
		     matrix has been interchanged with row IPIV(i).

	   JPIV

		     JPIV is INTEGER array, dimension (N).
		     The pivot indices; for 1 <= j <= N, column j of the
		     matrix has been interchanged with column JPIV(j).

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   September 2012

       Further Details:
	   This routine is a further developed implementation of algorithm BSOLVE in [1] using complete pivoting in the LU factorization.

       Contributors:
	   Bo Kagstrom and Peter Poromaa, Department of Computing Science, Umea University, S-901 87 Umea, Sweden.

       References:

	     [1] Bo Kagstrom and Lars Westin,
		 Generalized Schur Methods with Condition Estimators for
		 Solving the Generalized Sylvester Equation, IEEE Transactions
		 on Automatic Control, Vol. 34, No. 7, July 1989, pp 745-751.

	     [2] Peter Poromaa,
		 On Efficient and Robust Estimators for the Separation
		 between two Regular Matrix Pairs with Applications in
		 Condition Estimation. Report IMINF-95.05, Departement of
		 Computing Science, Umea University, S-901 87 Umea, Sweden, 1995.

       Definition at line 171 of file dlatdf.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       dlatdf.f(3)