
dlacn2.f(3) LAPACK dlacn2.f(3)
NAME
dlacn2.f 
SYNOPSIS
Functions/Subroutines
subroutine dlacn2 (N, V, X, ISGN, EST, KASE, ISAVE)
DLACN2 estimates the 1norm of a square matrix, using reverse communication for
evaluating matrixvector products.
Function/Subroutine Documentation
subroutine dlacn2 (integerN, double precision, dimension( * )V, double precision, dimension( *
)X, integer, dimension( * )ISGN, double precisionEST, integerKASE, integer, dimension( 3
)ISAVE)
DLACN2 estimates the 1norm of a square matrix, using reverse communication for evaluating
matrixvector products.
Purpose:
DLACN2 estimates the 1norm of a square, real matrix A.
Reverse communication is used for evaluating matrixvector products.
Parameters:
N
N is INTEGER
The order of the matrix. N >= 1.
V
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
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 recalled with all the other parameters
unchanged.
ISGN
ISGN is INTEGER array, dimension (N)
EST
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
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
ISAVE is INTEGER array, dimension (3)
ISAVE is used to save variables between calls to DLACN2
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Further Details:
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:
DLACON DLACN2
JUMP ISAVE(1)
J ISAVE(2)
ITER ISAVE(3)
Contributors:
Nick Higham, University of Manchester
References:
N.J. Higham, 'FORTRAN codes for estimating the onenorm of
a real or complex matrix, with applications to condition estimation', ACM Trans.
Math. Soft., vol. 14, no. 4, pp. 381396, December 1988.
Definition at line 137 of file dlacn2.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dlacn2.f(3) 
