clacon3lapack
Estimates the 1-norm of a square, complex matrix a
Usage
- SUBROUTINE CLACON(
-
N, V, X, EST, KASE )
- INTEGER
-
KASE, N
- REAL
-
EST
- COMPLEX
-
V( N ), X( N )
Purpose
CLACON 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 array, dimension (N)
-
On the final return, V = A*W, where EST = norm(V)/norm(W) (W is not returned).
- X (input/output) COMPLEX 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 CLACON must be re-called with all the other parameters unchanged.
- EST (input/output) REAL
-
On entry with KASE = 1 or 2 and JUMP = 3, EST should be unchanged from the previous call to CLACON. On exit, EST is an estimate (a lower bound) for norm(A).
- KASE (input/output) INTEGER
-
On the initial call to CLACON, 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 CLACON, 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