CLACN2(1) LAPACK auxiliary routine (version 3.2) CLACN2(1)NAME
CLACN2 - estimates the 1-norm of a square, complex matrix A
SYNOPSIS
SUBROUTINE CLACN2( N, V, X, EST, KASE, ISAVE )
INTEGER KASE, N
REAL EST
INTEGER ISAVE( 3 )
COMPLEX V( * ), X( * )
PURPOSE
CLACN2 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 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
parameters unchanged.
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
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 CLACON, which uses the array ISAVE in
place of a SAVE statement, as follows:
CLACON CLACN2
JUMP ISAVE(1)
J ISAVE(2)
ITER ISAVE(3)
LAPACK auxiliary routine (versioNovember 2008 CLACN2(1)