_TRBAK1(3F)_TRBAK1(3F)NAME
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
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
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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