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

# dlacon(3lapack)

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

## NAME

DLACON - estimates the 1-norm of a square, real matrix A

## SYNOPSIS

- SUBROUTINE DLACON(

  N, V, X, ISGN, EST, KASE )

- INTEGER

  KASE, N

- DOUBLE

  PRECISION EST

- INTEGER

  ISGN( \* )

- DOUBLE

  PRECISION V( \* ), X( \* )

## PURPOSE

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

## ARGUMENTS

- N (input) INTEGER

  The order of the matrix.  N \>= 1.

- V (workspace) DOUBLE PRECISION array, dimension (N)

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

- X (input/output) DOUBLE PRECISION array, dimension (N)

  On an intermediate return, X should be overwritten by A \* X,   if KASE=1, A' \* X,  if KASE=2, and DLACON must be re-called with all the other parameters unchanged.

- ISGN (workspace) INTEGER array, dimension (N)

  - EST (input/output) 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).

- KASE (input/output) 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' \* X. On the final return from DLACON, KASE will again be 0.

## FURTHER DETAILS

Contributed by Nick Higham, University of Manchester.\
 Originally named SONEST, 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.