?lacn2

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 4/28/2026

Version

Public

Estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

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 )

slacn2 dlacn2 clacn2 zlacn2

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

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.

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 A^:code:`T` * x for real flavors and A * x or A^:code:`H` * 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.

No return value.