*> \brief \b ZLACON estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products. * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download ZLACON + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE ZLACON( N, V, X, EST, KASE ) * * .. Scalar Arguments .. * INTEGER KASE, N * DOUBLE PRECISION EST * .. * .. Array Arguments .. * COMPLEX*16 V( N ), X( N ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> ZLACON estimates the 1-norm of a square, complex matrix A. *> Reverse communication is used for evaluating matrix-vector products. *> \endverbatim * * Arguments: * ========== * *> \param[in] N *> \verbatim *> N is INTEGER *> The order of the matrix. N >= 1. *> \endverbatim *> *> \param[out] V *> \verbatim *> V is COMPLEX*16 array, dimension (N) *> On the final return, V = A*W, where EST = norm(V)/norm(W) *> (W is not returned). *> \endverbatim *> *> \param[in,out] X *> \verbatim *> X is COMPLEX*16 array, dimension (N) *> On an intermediate return, X should be overwritten by *> A * X, if KASE=1, *> A**H * X, if KASE=2, *> where A**H is the conjugate transpose of A, and ZLACON must be *> re-called with all the other parameters unchanged. *> \endverbatim *> *> \param[in,out] EST *> \verbatim *> EST is DOUBLE PRECISION *> On entry with KASE = 1 or 2 and JUMP = 3, EST should be *> unchanged from the previous call to ZLACON. *> On exit, EST is an estimate (a lower bound) for norm(A). *> \endverbatim *> *> \param[in,out] KASE *> \verbatim *> KASE is INTEGER *> On the initial call to ZLACON, 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**H * X. *> On the final return from ZLACON, KASE will again be 0. *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date December 2016 * *> \ingroup complex16OTHERauxiliary * *> \par Further Details: * ===================== *> *> Originally named CONEST, dated March 16, 1988. \n *> Last modified: April, 1999 * *> \par Contributors: * ================== *> *> Nick Higham, University of Manchester * *> \par References: * ================ *> *> N.J. Higham, "FORTRAN codes for estimating the one-norm of *> a real or complex matrix, with applications to condition estimation", *> ACM Trans. Math. Soft., vol. 14, no. 4, pp. 381-396, December 1988. *> * ===================================================================== SUBROUTINE ZLACON( N, V, X, EST, KASE ) * * -- LAPACK auxiliary routine (version 3.7.0) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * December 2016 * * .. Scalar Arguments .. INTEGER KASE, N DOUBLE PRECISION EST * .. * .. Array Arguments .. COMPLEX*16 V( N ), X( N ) * .. * * ===================================================================== * * .. Parameters .. INTEGER ITMAX PARAMETER ( ITMAX = 5 ) DOUBLE PRECISION ONE, TWO PARAMETER ( ONE = 1.0D0, TWO = 2.0D0 ) COMPLEX*16 CZERO, CONE PARAMETER ( CZERO = ( 0.0D0, 0.0D0 ), \$ CONE = ( 1.0D0, 0.0D0 ) ) * .. * .. Local Scalars .. INTEGER I, ITER, J, JLAST, JUMP DOUBLE PRECISION ABSXI, ALTSGN, ESTOLD, SAFMIN, TEMP * .. * .. External Functions .. INTEGER IZMAX1 DOUBLE PRECISION DLAMCH, DZSUM1 EXTERNAL IZMAX1, DLAMCH, DZSUM1 * .. * .. External Subroutines .. EXTERNAL ZCOPY * .. * .. Intrinsic Functions .. INTRINSIC ABS, DBLE, DCMPLX, DIMAG * .. * .. Save statement .. SAVE * .. * .. Executable Statements .. * SAFMIN = DLAMCH( 'Safe minimum' ) IF( KASE.EQ.0 ) THEN DO 10 I = 1, N X( I ) = DCMPLX( ONE / DBLE( N ) ) 10 CONTINUE KASE = 1 JUMP = 1 RETURN END IF * GO TO ( 20, 40, 70, 90, 120 )JUMP * * ................ ENTRY (JUMP = 1) * FIRST ITERATION. X HAS BEEN OVERWRITTEN BY A*X. * 20 CONTINUE IF( N.EQ.1 ) THEN V( 1 ) = X( 1 ) EST = ABS( V( 1 ) ) * ... QUIT GO TO 130 END IF EST = DZSUM1( N, X, 1 ) * DO 30 I = 1, N ABSXI = ABS( X( I ) ) IF( ABSXI.GT.SAFMIN ) THEN X( I ) = DCMPLX( DBLE( X( I ) ) / ABSXI, \$ DIMAG( X( I ) ) / ABSXI ) ELSE X( I ) = CONE END IF 30 CONTINUE KASE = 2 JUMP = 2 RETURN * * ................ ENTRY (JUMP = 2) * FIRST ITERATION. X HAS BEEN OVERWRITTEN BY CTRANS(A)*X. * 40 CONTINUE J = IZMAX1( N, X, 1 ) ITER = 2 * * MAIN LOOP - ITERATIONS 2,3,...,ITMAX. * 50 CONTINUE DO 60 I = 1, N X( I ) = CZERO 60 CONTINUE X( J ) = CONE KASE = 1 JUMP = 3 RETURN * * ................ ENTRY (JUMP = 3) * X HAS BEEN OVERWRITTEN BY A*X. * 70 CONTINUE CALL ZCOPY( N, X, 1, V, 1 ) ESTOLD = EST EST = DZSUM1( N, V, 1 ) * * TEST FOR CYCLING. IF( EST.LE.ESTOLD ) \$ GO TO 100 * DO 80 I = 1, N ABSXI = ABS( X( I ) ) IF( ABSXI.GT.SAFMIN ) THEN X( I ) = DCMPLX( DBLE( X( I ) ) / ABSXI, \$ DIMAG( X( I ) ) / ABSXI ) ELSE X( I ) = CONE END IF 80 CONTINUE KASE = 2 JUMP = 4 RETURN * * ................ ENTRY (JUMP = 4) * X HAS BEEN OVERWRITTEN BY CTRANS(A)*X. * 90 CONTINUE JLAST = J J = IZMAX1( N, X, 1 ) IF( ( ABS( X( JLAST ) ).NE.ABS( X( J ) ) ) .AND. \$ ( ITER.LT.ITMAX ) ) THEN ITER = ITER + 1 GO TO 50 END IF * * ITERATION COMPLETE. FINAL STAGE. * 100 CONTINUE ALTSGN = ONE DO 110 I = 1, N X( I ) = DCMPLX( ALTSGN*( ONE+DBLE( I-1 ) / DBLE( N-1 ) ) ) ALTSGN = -ALTSGN 110 CONTINUE KASE = 1 JUMP = 5 RETURN * * ................ ENTRY (JUMP = 5) * X HAS BEEN OVERWRITTEN BY A*X. * 120 CONTINUE TEMP = TWO*( DZSUM1( N, X, 1 ) / DBLE( 3*N ) ) IF( TEMP.GT.EST ) THEN CALL ZCOPY( N, X, 1, V, 1 ) EST = TEMP END IF * 130 CONTINUE KASE = 0 RETURN * * End of ZLACON * END