*> \brief \b CLACN2 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 CLACN2 + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE CLACN2( N, V, X, EST, KASE, ISAVE ) * * .. Scalar Arguments .. * INTEGER KASE, N * REAL EST * .. * .. Array Arguments .. * INTEGER ISAVE( 3 ) * COMPLEX V( * ), X( * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> CLACN2 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 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 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 CLACN2 must be *> re-called with all the other parameters unchanged. *> \endverbatim *> *> \param[in,out] EST *> \verbatim *> EST is REAL *> On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be *> unchanged from the previous call to CLACN2. *> 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 CLACN2, 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 CLACN2, KASE will again be 0. *> \endverbatim *> *> \param[in,out] ISAVE *> \verbatim *> ISAVE is INTEGER array, dimension (3) *> ISAVE is used to save variables between calls to SLACN2 *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \ingroup complexOTHERauxiliary * *> \par Further Details: * ===================== *> *> \verbatim *> *> Originally named CONEST, dated March 16, 1988. *> *> Last modified: April, 1999 *> *> This is a thread safe version of CLACON, which uses the array ISAVE *> in place of a SAVE statement, as follows: *> *> CLACON CLACN2 *> JUMP ISAVE(1) *> J ISAVE(2) *> ITER ISAVE(3) *> \endverbatim * *> \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 CLACN2( N, V, X, EST, KASE, ISAVE ) * * -- LAPACK auxiliary routine -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * * .. Scalar Arguments .. INTEGER KASE, N REAL EST * .. * .. Array Arguments .. INTEGER ISAVE( 3 ) COMPLEX V( * ), X( * ) * .. * * ===================================================================== * * .. Parameters .. INTEGER ITMAX PARAMETER ( ITMAX = 5 ) REAL ONE, TWO PARAMETER ( ONE = 1.0E0, TWO = 2.0E0 ) COMPLEX CZERO, CONE PARAMETER ( CZERO = ( 0.0E0, 0.0E0 ), $ CONE = ( 1.0E0, 0.0E0 ) ) * .. * .. Local Scalars .. INTEGER I, JLAST REAL ABSXI, ALTSGN, ESTOLD, SAFMIN, TEMP * .. * .. External Functions .. INTEGER ICMAX1 REAL SCSUM1, SLAMCH EXTERNAL ICMAX1, SCSUM1, SLAMCH * .. * .. External Subroutines .. EXTERNAL CCOPY * .. * .. Intrinsic Functions .. INTRINSIC ABS, AIMAG, CMPLX, REAL * .. * .. Executable Statements .. * SAFMIN = SLAMCH( 'Safe minimum' ) IF( KASE.EQ.0 ) THEN DO 10 I = 1, N X( I ) = CMPLX( ONE / REAL( N ) ) 10 CONTINUE KASE = 1 ISAVE( 1 ) = 1 RETURN END IF * GO TO ( 20, 40, 70, 90, 120 )ISAVE( 1 ) * * ................ ENTRY (ISAVE( 1 ) = 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 = SCSUM1( N, X, 1 ) * DO 30 I = 1, N ABSXI = ABS( X( I ) ) IF( ABSXI.GT.SAFMIN ) THEN X( I ) = CMPLX( REAL( X( I ) ) / ABSXI, $ AIMAG( X( I ) ) / ABSXI ) ELSE X( I ) = CONE END IF 30 CONTINUE KASE = 2 ISAVE( 1 ) = 2 RETURN * * ................ ENTRY (ISAVE( 1 ) = 2) * FIRST ITERATION. X HAS BEEN OVERWRITTEN BY CTRANS(A)*X. * 40 CONTINUE ISAVE( 2 ) = ICMAX1( N, X, 1 ) ISAVE( 3 ) = 2 * * MAIN LOOP - ITERATIONS 2,3,...,ITMAX. * 50 CONTINUE DO 60 I = 1, N X( I ) = CZERO 60 CONTINUE X( ISAVE( 2 ) ) = CONE KASE = 1 ISAVE( 1 ) = 3 RETURN * * ................ ENTRY (ISAVE( 1 ) = 3) * X HAS BEEN OVERWRITTEN BY A*X. * 70 CONTINUE CALL CCOPY( N, X, 1, V, 1 ) ESTOLD = EST EST = SCSUM1( 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 ) = CMPLX( REAL( X( I ) ) / ABSXI, $ AIMAG( X( I ) ) / ABSXI ) ELSE X( I ) = CONE END IF 80 CONTINUE KASE = 2 ISAVE( 1 ) = 4 RETURN * * ................ ENTRY (ISAVE( 1 ) = 4) * X HAS BEEN OVERWRITTEN BY CTRANS(A)*X. * 90 CONTINUE JLAST = ISAVE( 2 ) ISAVE( 2 ) = ICMAX1( N, X, 1 ) IF( ( ABS( X( JLAST ) ).NE.ABS( X( ISAVE( 2 ) ) ) ) .AND. $ ( ISAVE( 3 ).LT.ITMAX ) ) THEN ISAVE( 3 ) = ISAVE( 3 ) + 1 GO TO 50 END IF * * ITERATION COMPLETE. FINAL STAGE. * 100 CONTINUE ALTSGN = ONE DO 110 I = 1, N X( I ) = CMPLX( ALTSGN*( ONE + REAL( I-1 ) / REAL( N-1 ) ) ) ALTSGN = -ALTSGN 110 CONTINUE KASE = 1 ISAVE( 1 ) = 5 RETURN * * ................ ENTRY (ISAVE( 1 ) = 5) * X HAS BEEN OVERWRITTEN BY A*X. * 120 CONTINUE TEMP = TWO*( SCSUM1( N, X, 1 ) / REAL( 3*N ) ) IF( TEMP.GT.EST ) THEN CALL CCOPY( N, X, 1, V, 1 ) EST = TEMP END IF * 130 CONTINUE KASE = 0 RETURN * * End of CLACN2 * END