#include "clapack.h"
#include "f2cP.h"

/* Table of constant values */

static integer c__1 = 1;
static double c_b11 = 1.;

/* Subroutine */ int dlacn2_(integer *n, double *v, double *x, 
	integer *isgn, double *est, integer *kase, integer *isave)
{
    /* System generated locals */
    integer i__1;
    double d__1;

    /* Local variables */
    integer i__;
    double temp;
    integer jlast;
    double altsgn, estold;


/*  -- LAPACK auxiliary routine (version 3.1) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/*     November 2006 */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  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 .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
/*     .. Executable Statements .. */

    /* Parameter adjustments */
    --isave;
    --isgn;
    --x;
    --v;

    /* Function Body */
    if (*kase == 0) {
	i__1 = *n;
	for (i__ = 1; i__ <= i__1; ++i__) {
	    x[i__] = 1. / (double) (*n);
/* L10: */
	}
	*kase = 1;
	isave[1] = 1;
	return 0;
    }

    switch (isave[1]) {
	case 1:  goto L20;
	case 2:  goto L40;
	case 3:  goto L70;
	case 4:  goto L110;
	case 5:  goto L140;
    }

/*     ................ ENTRY   (ISAVE( 1 ) = 1) */
/*     FIRST ITERATION.  X HAS BEEN OVERWRITTEN BY A*X. */

L20:
    if (*n == 1) {
	v[1] = x[1];
	*est = abs(v[1]);
/*        ... QUIT */
	goto L150;
    }
    *est = dasum_(n, &x[1], &c__1);

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	x[i__] = d_sign(&c_b11, &x[i__]);
	isgn[i__] = i_dnnt(&x[i__]);
/* L30: */
    }
    *kase = 2;
    isave[1] = 2;
    return 0;

/*     ................ ENTRY   (ISAVE( 1 ) = 2) */
/*     FIRST ITERATION.  X HAS BEEN OVERWRITTEN BY TRANSPOSE(A)*X. */

L40:
    isave[2] = idamax_(n, &x[1], &c__1);
    isave[3] = 2;

/*     MAIN LOOP - ITERATIONS 2,3,...,ITMAX. */

L50:
    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	x[i__] = 0.;
/* L60: */
    }
    x[isave[2]] = 1.;
    *kase = 1;
    isave[1] = 3;
    return 0;

/*     ................ ENTRY   (ISAVE( 1 ) = 3) */
/*     X HAS BEEN OVERWRITTEN BY A*X. */

L70:
    dcopy_(n, &x[1], &c__1, &v[1], &c__1);
    estold = *est;
    *est = dasum_(n, &v[1], &c__1);
    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	d__1 = d_sign(&c_b11, &x[i__]);
	if (i_dnnt(&d__1) != isgn[i__]) {
	    goto L90;
	}
/* L80: */
    }
/*     REPEATED SIGN VECTOR DETECTED, HENCE ALGORITHM HAS CONVERGED. */
    goto L120;

L90:
/*     TEST FOR CYCLING. */
    if (*est <= estold) {
	goto L120;
    }

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	x[i__] = d_sign(&c_b11, &x[i__]);
	isgn[i__] = i_dnnt(&x[i__]);
/* L100: */
    }
    *kase = 2;
    isave[1] = 4;
    return 0;

/*     ................ ENTRY   (ISAVE( 1 ) = 4) */
/*     X HAS BEEN OVERWRITTEN BY TRANSPOSE(A)*X. */

L110:
    jlast = isave[2];
    isave[2] = idamax_(n, &x[1], &c__1);
    if (x[jlast] != (d__1 = x[isave[2]], abs(d__1)) && isave[3] < 5) {
	++isave[3];
	goto L50;
    }

/*     ITERATION COMPLETE.  FINAL STAGE. */

L120:
    altsgn = 1.;
    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	x[i__] = altsgn * ((double) (i__ - 1) / (double) (*n - 1) + 
		1.);
	altsgn = -altsgn;
/* L130: */
    }
    *kase = 1;
    isave[1] = 5;
    return 0;

/*     ................ ENTRY   (ISAVE( 1 ) = 5) */
/*     X HAS BEEN OVERWRITTEN BY A*X. */

L140:
    temp = dasum_(n, &x[1], &c__1) / (double) (*n * 3) * 2.;
    if (temp > *est) {
	dcopy_(n, &x[1], &c__1, &v[1], &c__1);
	*est = temp;
    }

L150:
    *kase = 0;
    return 0;

/*     End of DLACN2 */

} /* dlacn2_ */
