Slacon.f -
subroutine slacon (N, V, X, ISGN, EST, KASE)
SLACON estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.
SLACON estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.
Purpose:
SLACON estimates the 1-norm of a square, real matrix A. Reverse communication is used for evaluating matrix-vector products.
Parameters:
N
N is INTEGER
The order of the matrix. N >= 1.
V
V is REAL array, dimension (N)
On the final return, V = A*W, where EST = norm(V)/norm(W)
(W is not returned).
X
X is REAL array, dimension (N)
On an intermediate return, X should be overwritten by
A * X, if KASE=1,
A**T * X, if KASE=2,
and SLACON must be re-called with all the other parameters
unchanged.
ISGN
ISGN is INTEGER array, dimension (N)
EST
EST is REAL
On entry with KASE = 1 or 2 and JUMP = 3, EST should be
unchanged from the previous call to SLACON.
On exit, EST is an estimate (a lower bound) for norm(A).
KASE
KASE is INTEGER
On the initial call to SLACON, 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 SLACON, KASE will again be 0.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Contributors:
Nick Higham, University of Manchester.
Originally named SONEST, dated March 16, 1988.
References:
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 116 of file slacon.f.
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