_COMQR(3F)_COMQR(3F)NAME
COMQR, SCOMQR - EISPACK routine. This subroutine finds the
eigenvalues of a COMPLEX upper Hessenberg matrix by the QR method.
SYNOPSYS
subroutine comqr(nm, n, low, igh, hr, hi, wr, wi, ierr)
integer nm, n, low, igh, ierr
double precision hr(nm,n), hi(nm,n), wr(n), wi(n)
subroutine scomqr(nm, n, low, igh, hr, hi, wr, wi, ierr)
integer nm, n, low, igh, ierr
real hr(nm,n), hi(nm,n), wr(n), wi(n)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.
LOW and IGH are integers determined by the balancing subroutine CBAL.
If CBAL has not been used, set LOW=1, IGH=N.
HR and HI contain the real and imaginary parts, respectively, of the
complex upper Hessenberg matrix. Their lower triangles below the
subdiagonal contain information about the unitary transformations used in
the reduction by CORTH, if performed. On OUTPUT The upper Hessenberg
portions of HR and HI have been destroyed. Therefore, they must be saved
before calling COMQR if subsequent calculation of eigenvectors is to be
performed.
WR and WI contain the real and imaginary parts, respectively, of the
eigenvalues. If an error exit is made, the eigenvalues should be correct
for indices IERR+1,...,N.
IERR is set to ZERO for normal return, J if the J-th
eigenvalue has not been
determined after a total of 30*N iterations. Calls CSROOT for complex
square root. Calls PYTHAG(A,B) for sqrt(A**2 + B**2). Calls CDIV for
complex division. Questions and comments should be directed to B. S.
Garbow, APPLIED MATHEMATICS DIVISION, ARGONNE NATIONAL LABORATORY
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