SLACN2
November 2006
Purpose
SLACN2 estimates the 1-norm of a square, real matrix A.
Reverse communication is used for evaluating matrix-vector products.
Reverse communication is used for evaluating matrix-vector products.
Arguments
| N |
(input) INTEGER
The order of the matrix. N >= 1.
|
| V |
(workspace) REAL array, dimension (N)
On the final return, V = A*W, where EST = norm(V)/norm(W)
(W is not returned). |
| X |
(input/output) REAL array, dimension (N)
On an intermediate return, X should be overwritten by
A * X, if KASE=1, A**T * X, if KASE=2, and SLACN2 must be re-called with all the other parameters unchanged. |
| ISGN |
(workspace) INTEGER array, dimension (N)
|
| EST |
(input/output) REAL
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to SLACN2. On exit, EST is an estimate (a lower bound) for norm(A). |
| KASE |
(input/output) INTEGER
On the initial call to SLACN2, 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 SLACN2, KASE will again be 0. |
| ISAVE |
(input/output) INTEGER array, dimension (3)
ISAVE is used to save variables between calls to SLACN2
|
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.
This is a thread safe version of SLACON, which uses the array ISAVE
in place of a SAVE statement, as follows:
SLACON SLACN2
JUMP ISAVE(1)
J ISAVE(2)
ITER ISAVE(3)
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.
This is a thread safe version of SLACON, which uses the array ISAVE
in place of a SAVE statement, as follows:
SLACON SLACN2
JUMP ISAVE(1)
J ISAVE(2)
ITER ISAVE(3)