DGGBAK man page on IRIX

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DGGBAK(3F)							    DGGBAK(3F)

NAME
     DGGBAK - form the right or left eigenvectors of a real generalized
     eigenvalue problem A*x = lambda*B*x, by backward transformation on the
     computed eigenvectors of the balanced pair of matrices output by DGGBAL

SYNOPSIS
     SUBROUTINE DGGBAK( JOB, SIDE, N, ILO, IHI, LSCALE, RSCALE, M, V, LDV,
			INFO )

	 CHARACTER	JOB, SIDE

	 INTEGER	IHI, ILO, INFO, LDV, M, N

	 DOUBLE		PRECISION LSCALE( * ), RSCALE( * ), V( LDV, * )

PURPOSE
     DGGBAK forms the right or left eigenvectors of a real generalized
     eigenvalue problem A*x = lambda*B*x, by backward transformation on the
     computed eigenvectors of the balanced pair of matrices output by DGGBAL.

ARGUMENTS
     JOB     (input) CHARACTER*1
	     Specifies the type of backward transformation required:
	     = 'N':  do nothing, return immediately;
	     = 'P':  do backward transformation for permutation only;
	     = 'S':  do backward transformation for scaling only;
	     = 'B':  do backward transformations for both permutation and
	     scaling.  JOB must be the same as the argument JOB supplied to
	     DGGBAL.

     SIDE    (input) CHARACTER*1
	     = 'R':  V contains right eigenvectors;
	     = 'L':  V contains left eigenvectors.

     N	     (input) INTEGER
	     The number of rows of the matrix V.  N >= 0.

     ILO     (input) INTEGER
	     IHI     (input) INTEGER The integers ILO and IHI determined by
	     DGGBAL.  1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.

     LSCALE  (input) DOUBLE PRECISION array, dimension (N)
	     Details of the permutations and/or scaling factors applied to the
	     left side of A and B, as returned by DGGBAL.

     RSCALE  (input) DOUBLE PRECISION array, dimension (N)
	     Details of the permutations and/or scaling factors applied to the
	     right side of A and B, as returned by DGGBAL.

									Page 1

DGGBAK(3F)							    DGGBAK(3F)

     M	     (input) INTEGER
	     The number of columns of the matrix V.  M >= 0.

     V	     (input/output) DOUBLE PRECISION array, dimension (LDV,M)
	     On entry, the matrix of right or left eigenvectors to be
	     transformed, as returned by DTGEVC.  On exit, V is overwritten by
	     the transformed eigenvectors.

     LDV     (input) INTEGER
	     The leading dimension of the matrix V. LDV >= max(1,N).

     INFO    (output) INTEGER
	     = 0:  successful exit.
	     < 0:  if INFO = -i, the i-th argument had an illegal value.

FURTHER DETAILS
     See R.C. Ward, Balancing the generalized eigenvalue problem,
		    SIAM J. Sci. Stat. Comp. 2 (1981), 141-152.

									Page 2

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