LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

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Functions/Subroutines  
subroutine  dlacn2 (N, V, X, ISGN, EST, KASE, ISAVE) 
DLACN2 estimates the 1norm of a square matrix, using reverse communication for evaluating matrixvector products. 
subroutine dlacn2  (  integer  N, 
double precision, dimension( * )  V,  
double precision, dimension( * )  X,  
integer, dimension( * )  ISGN,  
double precision  EST,  
integer  KASE,  
integer, dimension( 3 )  ISAVE  
) 
DLACN2 estimates the 1norm of a square matrix, using reverse communication for evaluating matrixvector products.
Download DLACN2 + dependencies [TGZ] [ZIP] [TXT]DLACN2 estimates the 1norm of a square, real matrix A. Reverse communication is used for evaluating matrixvector products.
[in]  N  N is INTEGER The order of the matrix. N >= 1. 
[out]  V  V is DOUBLE PRECISION array, dimension (N) On the final return, V = A*W, where EST = norm(V)/norm(W) (W is not returned). 
[in,out]  X  X is DOUBLE PRECISION array, dimension (N) On an intermediate return, X should be overwritten by A * X, if KASE=1, A**T * X, if KASE=2, and DLACN2 must be recalled with all the other parameters unchanged. 
[out]  ISGN  ISGN is INTEGER array, dimension (N) 
[in,out]  EST  EST is DOUBLE PRECISION On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be unchanged from the previous call to DLACN2. On exit, EST is an estimate (a lower bound) for norm(A). 
[in,out]  KASE  KASE is INTEGER On the initial call to DLACN2, 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 DLACN2, KASE will again be 0. 
[in,out]  ISAVE  ISAVE is INTEGER array, dimension (3) ISAVE is used to save variables between calls to DLACN2 
Originally named SONEST, dated March 16, 1988. This is a thread safe version of DLACON, which uses the array ISAVE in place of a SAVE statement, as follows: DLACON DLACN2 JUMP ISAVE(1) J ISAVE(2) ITER ISAVE(3)
Definition at line 137 of file dlacn2.f.