Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?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. Specifies the order of the matrix A. The value of n must be at least zero.
- 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 , A^{T}*x , if kase = 2 (for real flavors), A^{H}*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.
Return Values
No return value.