LAPACK  3.4.2
LAPACK: Linear Algebra PACKage
 All Files Functions Groups
Functions/Subroutines
dlacon.f File Reference

Go to the source code of this file.

Functions/Subroutines

subroutine dlacon (N, V, X, ISGN, EST, KASE)
 DLACON estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Function/Subroutine Documentation

subroutine dlacon ( integer  N,
double precision, dimension( * )  V,
double precision, dimension( * )  X,
integer, dimension( * )  ISGN,
double precision  EST,
integer  KASE 
)

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

Download DLACON + dependencies [TGZ] [ZIP] [TXT]
Purpose: 
 DLACON 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 DLACON 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 JUMP = 3, EST should be
         unchanged from the previous call to DLACON.
         On exit, EST is an estimate (a lower bound) for norm(A).
[in,out]KASE
          KASE is INTEGER
         On the initial call to DLACON, 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 DLACON, 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 dlacon.f.

Here is the call graph for this function: