Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?lacon
Estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.
Syntax
call slacon(n, v, x, isgn, est, kase)
call dlacon(n, v, x, isgn, est, kase)
call clacon(n, v, x, est, kase)
call zlacon(n, v, x, est, kase)
Include Files
mkl.fi
Description
The routine estimates the 1-norm of a square, real/complex matrix A . Reverse communication is used for evaluating matrix-vector products.
warning
The ?lacon routine is not thread-safe. It is deprecated and retained for the backward compatibility only. Use the thread-safe ?lacn2 (Estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.) routine instead.Input Parameters
- n
-
INTEGER. Specifies the order of the matrix A. The value of n must be at least zero.
- v , x
-
REAL for slacon DOUBLE PRECISION for dlacon COMPLEX for clacon DOUBLE COMPLEX for zlacon . Arrays, DIMENSION ( n ) each. v is a workspace array. x is used as input after an intermediate return.
- isgn
-
INTEGER . Workspace array, DIMENSION ( n ), used with real flavors only.
- est
-
REAL for slacon / clacon DOUBLE PRECISION for dlacon / zlacon An estimate that with kase =1 or 2 should be unchanged from the previous call to ?lacon .
- kase
-
INTEGER . On the initial call to ?lacon , kase should be 0.
Output Parameters
- est
-
REAL for slacon / clacon DOUBLE PRECISION for dlacon / zlacon An estimate (a lower bound) for norm( A ).
- kase
-
On an intermediate return, kase will be 1 or 2, indicating whether x should be overwritten by A * x or AT * x for real flavors and A * x or AH * x for complex flavors. On the final return from ?lacon , kase will again be 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 should be 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 ?lacon must be re-called with all the other parameters unchanged.