LAPACK  3.4.0
LAPACK: Linear Algebra PACKage
Functions/Subroutines
dlacn2.f File Reference

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Functions/Subroutines

subroutine DLACN2 (N, V, X, ISGN, EST, KASE, ISAVE)
 DLACN2

Function/Subroutine Documentation

subroutine DLACN2 ( INTEGER  N,
DOUBLE PRECISION, dimension( * )  V,
DOUBLE PRECISION, dimension( * )  X,
INTEGER, dimension( * )  ISGN,
DOUBLE PRECISION  EST,
INTEGER  KASE,
INTEGER, dimension( 3 )  ISAVE 
)

DLACN2

Download DLACN2 + dependencies [TGZ] [ZIP] [TXT]
Purpose: 

 DLACN2 estimates the 1-norm of a square, real matrix A.
 Reverse communication is used for evaluating matrix-vector products.
Parameters:
[in]N
          N is INTEGER
         The order of the matrix.  N >= 1.
[out]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).
[in,out]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.
[out]ISGN
          ISGN is INTEGER array, dimension (N)
[in,out]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).
[in,out]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.
[in,out]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:
November 2011
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.

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