SYNOPSIS

SUBROUTINE ZLACON(

N, V, X, EST, KASE )

    

INTEGER KASE, N

    

DOUBLE PRECISION EST

    

COMPLEX*16 V( N ), X( N )

PURPOSE

ZLACON estimates the 1-norm of a square, complex matrix A. Reverse communication is used for evaluating matrix-vector products.

ARGUMENTS

N (input) INTEGER

The order of the matrix. N >= 1.

V (workspace) COMPLEX*16 array, dimension (N)

On the final return, V = A*W, where EST = norm(V)/norm(W) (W is not returned).

X (input/output) COMPLEX*16 array, dimension (N)

On an intermediate return, X should be overwritten by A * X, if KASE=1, A' * X, if KASE=2, where A' is the conjugate transpose of A, and ZLACON must be re-called with all the other parameters unchanged.

EST (input/output) DOUBLE PRECISION

On entry with KASE = 1 or 2 and JUMP = 3, EST should be unchanged from the previous call to ZLACON. On exit, EST is an estimate (a lower bound) for norm(A).

KASE (input/output) INTEGER

On the initial call to ZLACON, 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' * X. On the final return from ZLACON, KASE will again be 0.

FURTHER DETAILS

Contributed by Nick Higham, University of Manchester.
Originally named CONEST, dated March 16, 1988.
Reference: 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. Last modified: April, 1999