_TRBAK1(3F)							   _TRBAK1(3F)

NAME    [Toc]    [Back]

     TRBAK1, STRBAK1  -	 EISPACK routine.  This	subroutine forms the
     eigenvectors of a REAL SYMMETRIC matrix by	back transforming those	of the
     corresponding symmetric tridiagonal matrix	determined by  TRED1.

SYNOPSYS    [Toc]    [Back]

	  subroutine  trbak1(nm, n, a, e, m, z)
	  integer	   nm, n, m
	  double precision a(nm,n), e(n), z(nm,m)

	  subroutine strbak1(nm, n, a, e, m, z)
	  integer	   nm, n, m
	  real		   a(nm,n), e(n), z(nm,m)

DESCRIPTION    [Toc]    [Back]

     On	Input

     NM	must be	set to the row dimension of two-dimensional array parameters
     as	declared in the	calling	program	dimension statement.

     N is the order of the matrix.

     A contains	information about the orthogonal trans-	formations used	in the
     reduction by  TRED1 in its	strict lower triangle.

     E contains	the subdiagonal	elements of the	tridiagonal matrix in its last
     N-1 positions.  E(1) is arbitrary.

     M is the number of	eigenvectors to	be back	transformed.

     Z contains	the eigenvectors to be back transformed	in its first M
     columns.  On Output

     Z contains	the transformed	eigenvectors in	its first M columns.  Note
     that TRBAK1 preserves vector Euclidean norms.  Questions and comments
     should be directed	to B. S. Garbow, APPLIED MATHEMATICS DIVISION, ARGONNE
     NATIONAL LABORATORY


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