ZLACN2(1) LAPACK auxiliary routine (version 3.2) ZLACN2(1)NAME
ZLACN2 - estimates the 1-norm of a square, complex matrix A
SYNOPSIS
SUBROUTINE ZLACN2( N, V, X, EST, KASE, ISAVE )
INTEGER KASE, N
DOUBLE PRECISION EST
INTEGER ISAVE( 3 )
COMPLEX*16 V( * ), X( * )
PURPOSE
ZLACN2 estimates the 1-norm of a square, complex matrix A. Reverse
communication is used for evaluating matrix-vector products.
ARGUMENTS
N (input) INTEGER
The order of the matrix. N >= 1.
V (workspace) COMPLEX*16 array, dimension (N)
On the final return, V = A*W, where EST = norm(V)/norm(W) (W
is not returned).
X (input/output) COMPLEX*16 array, dimension (N)
On an intermediate return, X should be overwritten by A * X,
if KASE=1, A' * X, if KASE=2, where A' is the conjugate trans‐
pose of A, and ZLACN2 must be re-called with all the other
parameters unchanged.
EST (input/output) DOUBLE PRECISION
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to ZLACN2. On exit, EST is an
estimate (a lower bound) for norm(A).
KASE (input/output) INTEGER
On the initial call to ZLACN2, KASE should be 0. On an interme‐
diate return, KASE will be 1 or 2, indicating whether X should
be overwritten by A * X or A' * X. On the final return from
ZLACN2, KASE will again be 0.
ISAVE (input/output) INTEGER array, dimension (3)
ISAVE is used to save variables between calls to ZLACN2
FURTHER DETAILS
Contributed by Nick Higham, University of Manchester.
Originally named CONEST, dated March 16, 1988.
Reference: N.J. Higham, "FORTRAN codes for estimating the one-norm of a
real or complex matrix, with applications to condition estimation", ACM
Trans. Math. Soft., vol. 14, no. 4, pp. 381-396, December 1988. Last
modified: April, 1999
This is a thread safe version of ZLACON, which uses the array ISAVE in
place of a SAVE statement, as follows:
ZLACON ZLACN2
JUMP ISAVE(1)
J ISAVE(2)
ITER ISAVE(3)
LAPACK auxiliary routine (versioNovember 2008 ZLACN2(1)