dlacn2.f(3) LAPACK dlacn2.f(3)
subroutine dlacn2 (N, V, X, ISGN, EST, KASE, ISAVE)
DLACN2 estimates the 1-norm of a square matrix, using reverse communication for
evaluating matrix-vector products.
subroutine dlacn2 (integerN, double precision, dimension( * )V, double precision, dimension( *
)X, integer, dimension( * )ISGN, double precisionEST, integerKASE, integer, dimension( 3
DLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating
DLACN2 estimates the 1-norm of a square, real matrix A.
Reverse communication is used for evaluating matrix-vector products.
N is INTEGER
The order of the matrix. N >= 1.
V is DOUBLE PRECISION array, dimension (N)
On the final return, V = A*W, where EST = norm(V)/norm(W)
(W is not returned).
X is DOUBLE PRECISION array, dimension (N)
On an intermediate return, X should be overwritten by
A * X, if KASE=1,
A**T * X, if KASE=2,
and DLACN2 must be re-called with all the other parameters
ISGN is INTEGER array, dimension (N)
EST is DOUBLE PRECISION
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to DLACN2.
On exit, EST is an estimate (a lower bound) for norm(A).
KASE is INTEGER
On the initial call to DLACN2, KASE should be 0.
On an intermediate return, KASE will be 1 or 2, indicating
whether X should be overwritten by A * X or A**T * X.
On the final return from DLACN2, KASE will again be 0.
ISAVE is INTEGER array, dimension (3)
ISAVE is used to save variables between calls to DLACN2
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
Originally named SONEST, dated March 16, 1988.
This is a thread safe version of DLACON, which uses the array ISAVE
in place of a SAVE statement, as follows:
Nick Higham, University of Manchester
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.
Definition at line 137 of file dlacn2.f.
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Version 3.4.2 Tue Sep 25 2012 dlacn2.f(3)