#include "blaswrap.h"
#include "f2c.h"

/* Subroutine */ int slacn2_(integer *n, real *v, real *x, integer *isgn, 
	real *est, integer *kase, integer *isave)
{
/*  -- LAPACK auxiliary routine (version 3.1) --   
       Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..   
       November 2006   


    Purpose   
    =======   

    SLACN2 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) REAL array, dimension (N)   
           On the final return, V = A*W,  where  EST = norm(V)/norm(W)   
           (W is not returned).   

    X      (input/output) REAL array, dimension (N)   
           On an intermediate return, X should be overwritten by   
                 A * X,   if KASE=1,   
                 A' * X,  if KASE=2,   
           and SLACN2 must be re-called with all the other parameters   
           unchanged.   

    ISGN   (workspace) INTEGER array, dimension (N)   

    EST    (input/output) REAL   
           On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be   
           unchanged from the previous call to SLACN2.   
           On exit, EST is an estimate (a lower bound) for norm(A).   

    KASE   (input/output) INTEGER   
           On the initial call to SLACN2, 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 SLACN2, KASE will again be 0.   

    ISAVE  (input/output) INTEGER array, dimension (3)   
           ISAVE is used to save variables between calls to SLACN2   

    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 SLACON, which uses the array ISAVE   
    in place of a SAVE statement, as follows:   

       SLACON     SLACN2   
        JUMP     ISAVE(1)   
        J        ISAVE(2)   
        ITER     ISAVE(3)   

    =====================================================================   


       Parameter adjustments */
    /* Table of constant values */
    static integer c__1 = 1;
    static real c_b11 = 1.f;
    
    /* System generated locals */
    integer i__1;
    real r__1;
    /* Builtin functions */
    double r_sign(real *, real *);
    integer i_nint(real *);
    /* Local variables */
    static integer i__;
    static real temp;
    static integer jlast;
    extern doublereal sasum_(integer *, real *, integer *);
    extern /* Subroutine */ int scopy_(integer *, real *, integer *, real *, 
	    integer *);
    extern integer isamax_(integer *, real *, integer *);
    static real altsgn, estold;


    --isave;
    --isgn;
    --x;
    --v;

    /* Function Body */
    if (*kase == 0) {
	i__1 = *n;
	for (i__ = 1; i__ <= i__1; ++i__) {
	    x[i__] = 1.f / (real) (*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 = dabs(v[1]);
/*        ... QUIT */
	goto L150;
    }
    *est = sasum_(n, &x[1], &c__1);

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	x[i__] = r_sign(&c_b11, &x[i__]);
	isgn[i__] = i_nint(&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] = isamax_(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.f;
/* L60: */
    }
    x[isave[2]] = 1.f;
    *kase = 1;
    isave[1] = 3;
    return 0;

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

L70:
    scopy_(n, &x[1], &c__1, &v[1], &c__1);
    estold = *est;
    *est = sasum_(n, &v[1], &c__1);
    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	r__1 = r_sign(&c_b11, &x[i__]);
	if (i_nint(&r__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__] = r_sign(&c_b11, &x[i__]);
	isgn[i__] = i_nint(&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] = isamax_(n, &x[1], &c__1);
    if (x[jlast] != (r__1 = x[isave[2]], dabs(r__1)) && isave[3] < 5) {
	++isave[3];
	goto L50;
    }

/*     ITERATION COMPLETE.  FINAL STAGE. */

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

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

L140:
    temp = sasum_(n, &x[1], &c__1) / (real) (*n * 3) * 2.f;
    if (temp > *est) {
	scopy_(n, &x[1], &c__1, &v[1], &c__1);
	*est = temp;
    }

L150:
    *kase = 0;
    return 0;

/*     End of SLACN2 */

} /* slacn2_ */