# dlacon.f - Man Page

SRC/dlacon.f

## Synopsis

### 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.

**Purpose:**

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

**Parameters***N*N is INTEGER The order of the matrix. N >= 1.

*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).

*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.

*ISGN*ISGN is INTEGER array, dimension (N)

*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).

*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.

**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 **114** of file **dlacon.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dlacon(3) is an alias of dlacon.f(3).