---
name: "zlacn2"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/zlacn2/3lapack"
---

# zlacn2(3lapack)

estimates the 1-norm of a square, complex matrix A

## NAME

ZLACN2 - estimates the 1-norm of a square, complex matrix A

## SYNOPSIS

- SUBROUTINE ZLACN2(

  N, V, X, EST, KASE, ISAVE )

- INTEGER

  KASE, N

- DOUBLE

  PRECISION EST

- INTEGER

  ISAVE( 3 )

- COMPLEX\*16

  V( \* ), X( \* )

## PURPOSE

ZLACN2 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 ZLACN2 must be re-called with all the other parameters unchanged.

- EST (input/output) DOUBLE PRECISION

  On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be unchanged from the previous call to ZLACN2. On exit, EST is an estimate (a lower bound) for norm(A).

- KASE (input/output) INTEGER

  On the initial call to ZLACN2, 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 ZLACN2, KASE will again be 0.

- ISAVE (input/output) INTEGER array, dimension (3)

  ISAVE is used to save variables between calls to ZLACN2

## 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\
 This is a thread safe version of ZLACON, which uses the array ISAVE in place of a SAVE statement, as follows:\
\
    ZLACON     ZLACN2\
\
     JUMP     ISAVE(1)\
\
     J        ISAVE(2)\
\
     ITER     ISAVE(3)\