dlacn2.f (3) Linux Manual Page

dlacn2.f –

Synopsis

Functions/Subroutines

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.

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 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Purpose:

 DLACN2 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 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 re-called 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 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.

Author

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