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+ SUBROUTINE DLACN2( N, V, X, ISGN, EST, KASE, ISAVE )
+*
+* -- LAPACK auxiliary routine (version 3.1) --
+* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
+* November 2006
+*
+* .. Scalar Arguments ..
+ INTEGER KASE, N
+ DOUBLE PRECISION EST
+* ..
+* .. Array Arguments ..
+ INTEGER ISGN( * ), ISAVE( 3 )
+ DOUBLE PRECISION V( * ), X( * )
+* ..
+*
+* Purpose
+* =======
+*
+* DLACN2 estimates the 1-norm of a square, real matrix A.
+* Reverse communication is used for evaluating matrix-vector products.
+*
+* Arguments
+* =========
+*
+* N (input) INTEGER
+* The order of the matrix. N >= 1.
+*
+* V (workspace) DOUBLE PRECISION array, dimension (N)
+* On the final return, V = A*W, where EST = norm(V)/norm(W)
+* (W is not returned).
+*
+* X (input/output) DOUBLE PRECISION array, dimension (N)
+* On an intermediate return, X should be overwritten by
+* A * X, if KASE=1,
+* A' * X, if KASE=2,
+* and DLACN2 must be re-called with all the other parameters
+* unchanged.
+*
+* ISGN (workspace) INTEGER array, dimension (N)
+*
+* EST (input/output) 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).
+*
+* KASE (input/output) 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' * X.
+* On the final return from DLACN2, KASE will again be 0.
+*
+* ISAVE (input/output) INTEGER array, dimension (3)
+* ISAVE is used to save variables between calls to DLACN2
+*
+* Further Details
+* ======= =======
+*
+* Contributed by Nick Higham, University of Manchester.
+* Originally named SONEST, dated March 16, 1988.
+*
+* Reference: 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.
+*
+* 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)
+*
+* =====================================================================
+*
+* .. Parameters ..
+ INTEGER ITMAX
+ PARAMETER ( ITMAX = 5 )
+ DOUBLE PRECISION ZERO, ONE, TWO
+ PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0, TWO = 2.0D+0 )
+* ..
+* .. Local Scalars ..
+ INTEGER I, JLAST
+ DOUBLE PRECISION ALTSGN, ESTOLD, TEMP
+* ..
+* .. External Functions ..
+ INTEGER IDAMAX
+ DOUBLE PRECISION DASUM
+ EXTERNAL IDAMAX, DASUM
+* ..
+* .. External Subroutines ..
+ EXTERNAL DCOPY
+* ..
+* .. Intrinsic Functions ..
+ INTRINSIC ABS, DBLE, NINT, SIGN
+* ..
+* .. Executable Statements ..
+*
+ IF( KASE.EQ.0 ) THEN
+ DO 10 I = 1, N
+ X( I ) = ONE / DBLE( N )
+ 10 CONTINUE
+ KASE = 1
+ ISAVE( 1 ) = 1
+ RETURN
+ END IF
+*
+ GO TO ( 20, 40, 70, 110, 140 )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 150
+ END IF
+ EST = DASUM( N, X, 1 )
+*
+ DO 30 I = 1, N
+ X( I ) = SIGN( ONE, X( I ) )
+ ISGN( I ) = NINT( X( I ) )
+ 30 CONTINUE
+ KASE = 2
+ ISAVE( 1 ) = 2
+ RETURN
+*
+* ................ ENTRY (ISAVE( 1 ) = 2)
+* FIRST ITERATION. X HAS BEEN OVERWRITTEN BY TRANSPOSE(A)*X.
+*
+ 40 CONTINUE
+ ISAVE( 2 ) = IDAMAX( N, X, 1 )
+ ISAVE( 3 ) = 2
+*
+* MAIN LOOP - ITERATIONS 2,3,...,ITMAX.
+*
+ 50 CONTINUE
+ DO 60 I = 1, N
+ X( I ) = ZERO
+ 60 CONTINUE
+ X( ISAVE( 2 ) ) = ONE
+ KASE = 1
+ ISAVE( 1 ) = 3
+ RETURN
+*
+* ................ ENTRY (ISAVE( 1 ) = 3)
+* X HAS BEEN OVERWRITTEN BY A*X.
+*
+ 70 CONTINUE
+ CALL DCOPY( N, X, 1, V, 1 )
+ ESTOLD = EST
+ EST = DASUM( N, V, 1 )
+ DO 80 I = 1, N
+ IF( NINT( SIGN( ONE, X( I ) ) ).NE.ISGN( I ) )
+ $ GO TO 90
+ 80 CONTINUE
+* REPEATED SIGN VECTOR DETECTED, HENCE ALGORITHM HAS CONVERGED.
+ GO TO 120
+*
+ 90 CONTINUE
+* TEST FOR CYCLING.
+ IF( EST.LE.ESTOLD )
+ $ GO TO 120
+*
+ DO 100 I = 1, N
+ X( I ) = SIGN( ONE, X( I ) )
+ ISGN( I ) = NINT( X( I ) )
+ 100 CONTINUE
+ KASE = 2
+ ISAVE( 1 ) = 4
+ RETURN
+*
+* ................ ENTRY (ISAVE( 1 ) = 4)
+* X HAS BEEN OVERWRITTEN BY TRANSPOSE(A)*X.
+*
+ 110 CONTINUE
+ JLAST = ISAVE( 2 )
+ ISAVE( 2 ) = IDAMAX( N, X, 1 )
+ IF( ( 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.
+*
+ 120 CONTINUE
+ ALTSGN = ONE
+ DO 130 I = 1, N
+ X( I ) = ALTSGN*( ONE+DBLE( I-1 ) / DBLE( N-1 ) )
+ ALTSGN = -ALTSGN
+ 130 CONTINUE
+ KASE = 1
+ ISAVE( 1 ) = 5
+ RETURN
+*
+* ................ ENTRY (ISAVE( 1 ) = 5)
+* X HAS BEEN OVERWRITTEN BY A*X.
+*
+ 140 CONTINUE
+ TEMP = TWO*( DASUM( N, X, 1 ) / DBLE( 3*N ) )
+ IF( TEMP.GT.EST ) THEN
+ CALL DCOPY( N, X, 1, V, 1 )
+ EST = TEMP
+ END IF
+*
+ 150 CONTINUE
+ KASE = 0
+ RETURN
+*
+* End of DLACN2
+*
+ END