Visible to Intel only — GUID: GUID-DBB012CA-94E8-423A-98D5-FB05C156484D
Visible to Intel only — GUID: GUID-DBB012CA-94E8-423A-98D5-FB05C156484D
?lacn2
Estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.
Syntax
call slacn2( n, v, x, isgn, est, kase, isave )
call dlacn2( n, v, x, isgn, est, kase, isave )
call clacn2( n, v, x, est, kase, isave )
call zlacn2( n, v, x, est, kase, isave )
Include Files
- mkl.fi
Description
The routine estimates the 1-norm of a square, real or complex matrix A. Reverse communication is used for evaluating matrix-vector products.
Input Parameters
- n
-
INTEGER. The order of the matrix A (n≥ 1).
- v, x
-
REAL for slacn2
DOUBLE PRECISION for dlacn2
COMPLEX for clacn2
DOUBLE COMPLEX for zlacn2.
Arrays, size (n) each.
v is a workspace array.
x is used as input after an intermediate return.
- isgn
-
INTEGER.
Workspace array, size (n), used with real flavors only.
- est
-
REAL for slacn2/clacn2
DOUBLE PRECISION for dlacn2/zlacn2
On entry with kase set to 1 or 2, and isave(1) = 1, est must be unchanged from the previous call to the routine.
- kase
-
INTEGER.
On the initial call to the routine, kase must be set to 0.
- isave
-
INTEGER. Array, size (3).
Contains variables from the previous call to the routine.
Output Parameters
- est
-
An estimate (a lower bound) for norm(A).
- kase
-
On an intermediate return, kase is set to 1 or 2, indicating whether x is overwritten by A*x or AT*x for real flavors and A*x or AH*x for complex flavors.
On the final return, kase is set to 0.
- v
-
On the final return, v = A*w, where est = norm(v)/norm(w) (w is not returned).
- x
-
On an intermediate return, x is overwritten by
A*x, if kase = 1,
AT*x, if kase = 2 (for real flavors),
AH*x, if kase = 2 (for complex flavors),
and the routine must be re-called with all the other parameters unchanged.
- isave
-
This parameter is used to save variables between calls to the routine.