CLACN2(1) LAPACK auxiliary routine (version 3.2) CLACN2(1)NAME
CLACN2 - estimates the 1-norm of a square, complex matrix A
SUBROUTINE CLACN2( N, V, X, EST, KASE, ISAVE )
INTEGER KASE, N
INTEGER ISAVE( 3 )
COMPLEX V( * ), X( * )
CLACN2 estimates the 1-norm of a square, complex matrix A. Reverse
communication is used for evaluating matrix-vector products.
N (input) INTEGER
The order of the matrix. N >= 1.
V (workspace) COMPLEX array, dimension (N)
On the final return, V = A*W, where EST = norm(V)/norm(W) (W
is not returned).
X (input/output) COMPLEX 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 CLACN2 must be re-called with all the other
EST (input/output) REAL
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to CLACN2. On exit, EST is an
estimate (a lower bound) for norm(A).
KASE (input/output) INTEGER
On the initial call to CLACN2, 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
CLACN2, KASE will again be 0.
ISAVE (input/output) INTEGER array, dimension (3)
ISAVE is used to save variables between calls to SLACN2
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 CLACON, which uses the array ISAVE in
place of a SAVE statement, as follows:
LAPACK auxiliary routine (versioNovember 2008 CLACN2(1)