/*  -- translated by f2c (version 20240504).
   You must link the resulting object file with libf2c:
	on Microsoft Windows system, link with libf2c.lib;
	on Linux or Unix systems, link with .../path/to/libf2c.a -lm
	or, if you install libf2c.a in a standard place, with -lf2c -lm
	-- in that order, at the end of the command line, as in
		cc *.o -lf2c -lm
	Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,

		http://www.netlib.org/f2c/libf2c.zip
*/

#include "f2c.h"

/* Table of constant values */

static integer c__4 = 4;
static integer c__1 = 1;
static integer c__16 = 16;
static integer c__0 = 0;

/* > \brief \b DLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2.   

    =========== DOCUMENTATION ===========   

   Online html documentation available at   
              http://www.netlib.org/lapack/explore-html/   

   > \htmlonly   
   > Download DLASY2 + dependencies   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlasy2.
f">   
   > [TGZ]</a>   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlasy2.
f">   
   > [ZIP]</a>   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlasy2.
f">   
   > [TXT]</a>   
   > \endhtmlonly   

    Definition:   
    ===========   

         SUBROUTINE DLASY2( LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR,   
                            LDTR, B, LDB, SCALE, X, LDX, XNORM, INFO )   

         LOGICAL            LTRANL, LTRANR   
         INTEGER            INFO, ISGN, LDB, LDTL, LDTR, LDX, N1, N2   
         DOUBLE PRECISION   SCALE, XNORM   
         DOUBLE PRECISION   B( LDB, * ), TL( LDTL, * ), TR( LDTR, * ),   
        $                   X( LDX, * )   


   > \par Purpose:   
    =============   
   >   
   > \verbatim   
   >   
   > DLASY2 solves for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in   
   >   
   >        op(TL)*X + ISGN*X*op(TR) = SCALE*B,   
   >   
   > where TL is N1 by N1, TR is N2 by N2, B is N1 by N2, and ISGN = 1 or   
   > -1.  op(T) = T or T**T, where T**T denotes the transpose of T.   
   > \endverbatim   

    Arguments:   
    ==========   

   > \param[in] LTRANL   
   > \verbatim   
   >          LTRANL is LOGICAL   
   >          On entry, LTRANL specifies the op(TL):   
   >             = .FALSE., op(TL) = TL,   
   >             = .TRUE., op(TL) = TL**T.   
   > \endverbatim   
   >   
   > \param[in] LTRANR   
   > \verbatim   
   >          LTRANR is LOGICAL   
   >          On entry, LTRANR specifies the op(TR):   
   >            = .FALSE., op(TR) = TR,   
   >            = .TRUE., op(TR) = TR**T.   
   > \endverbatim   
   >   
   > \param[in] ISGN   
   > \verbatim   
   >          ISGN is INTEGER   
   >          On entry, ISGN specifies the sign of the equation   
   >          as described before. ISGN may only be 1 or -1.   
   > \endverbatim   
   >   
   > \param[in] N1   
   > \verbatim   
   >          N1 is INTEGER   
   >          On entry, N1 specifies the order of matrix TL.   
   >          N1 may only be 0, 1 or 2.   
   > \endverbatim   
   >   
   > \param[in] N2   
   > \verbatim   
   >          N2 is INTEGER   
   >          On entry, N2 specifies the order of matrix TR.   
   >          N2 may only be 0, 1 or 2.   
   > \endverbatim   
   >   
   > \param[in] TL   
   > \verbatim   
   >          TL is DOUBLE PRECISION array, dimension (LDTL,2)   
   >          On entry, TL contains an N1 by N1 matrix.   
   > \endverbatim   
   >   
   > \param[in] LDTL   
   > \verbatim   
   >          LDTL is INTEGER   
   >          The leading dimension of the matrix TL. LDTL >= max(1,N1).   
   > \endverbatim   
   >   
   > \param[in] TR   
   > \verbatim   
   >          TR is DOUBLE PRECISION array, dimension (LDTR,2)   
   >          On entry, TR contains an N2 by N2 matrix.   
   > \endverbatim   
   >   
   > \param[in] LDTR   
   > \verbatim   
   >          LDTR is INTEGER   
   >          The leading dimension of the matrix TR. LDTR >= max(1,N2).   
   > \endverbatim   
   >   
   > \param[in] B   
   > \verbatim   
   >          B is DOUBLE PRECISION array, dimension (LDB,2)   
   >          On entry, the N1 by N2 matrix B contains the right-hand   
   >          side of the equation.   
   > \endverbatim   
   >   
   > \param[in] LDB   
   > \verbatim   
   >          LDB is INTEGER   
   >          The leading dimension of the matrix B. LDB >= max(1,N1).   
   > \endverbatim   
   >   
   > \param[out] SCALE   
   > \verbatim   
   >          SCALE is DOUBLE PRECISION   
   >          On exit, SCALE contains the scale factor. SCALE is chosen   
   >          less than or equal to 1 to prevent the solution overflowing.   
   > \endverbatim   
   >   
   > \param[out] X   
   > \verbatim   
   >          X is DOUBLE PRECISION array, dimension (LDX,2)   
   >          On exit, X contains the N1 by N2 solution.   
   > \endverbatim   
   >   
   > \param[in] LDX   
   > \verbatim   
   >          LDX is INTEGER   
   >          The leading dimension of the matrix X. LDX >= max(1,N1).   
   > \endverbatim   
   >   
   > \param[out] XNORM   
   > \verbatim   
   >          XNORM is DOUBLE PRECISION   
   >          On exit, XNORM is the infinity-norm of the solution.   
   > \endverbatim   
   >   
   > \param[out] INFO   
   > \verbatim   
   >          INFO is INTEGER   
   >          On exit, INFO is set to   
   >             0: successful exit.   
   >             1: TL and TR have too close eigenvalues, so TL or   
   >                TR is perturbed to get a nonsingular equation.   
   >          NOTE: In the interests of speed, this routine does not   
   >                check the inputs for errors.   
   > \endverbatim   

    Authors:   
    ========   

   > \author Univ. of Tennessee   
   > \author Univ. of California Berkeley   
   > \author Univ. of Colorado Denver   
   > \author NAG Ltd.   

   > \date September 2012   

   > \ingroup doubleSYauxiliary   

    =====================================================================   
   Subroutine */ int igraphdlasy2_(logical *ltranl, logical *ltranr, integer *isgn, 
	integer *n1, integer *n2, doublereal *tl, integer *ldtl, doublereal *
	tr, integer *ldtr, doublereal *b, integer *ldb, doublereal *scale, 
	doublereal *x, integer *ldx, doublereal *xnorm, integer *info)
{
    /* Initialized data */

    IGRAPH_F77_SAVE integer locu12[4] = { 3,4,1,2 };
    IGRAPH_F77_SAVE integer locl21[4] = { 2,1,4,3 };
    IGRAPH_F77_SAVE integer locu22[4] = { 4,3,2,1 };
    IGRAPH_F77_SAVE logical xswpiv[4] = { FALSE_,FALSE_,TRUE_,TRUE_ };
    IGRAPH_F77_SAVE logical bswpiv[4] = { FALSE_,TRUE_,FALSE_,TRUE_ };

    /* System generated locals */
    integer b_dim1, b_offset, tl_dim1, tl_offset, tr_dim1, tr_offset, x_dim1, 
	    x_offset;
    doublereal d__1, d__2, d__3, d__4, d__5, d__6, d__7, d__8;

    /* Local variables */
    integer i__, j, k;
    doublereal x2[2], l21, u11, u12;
    integer ip, jp;
    doublereal u22, t16[16]	/* was [4][4] */, gam, bet, eps, sgn, tmp[4], 
	    tau1, btmp[4], smin;
    integer ipiv;
    doublereal temp;
    integer jpiv[4];
    doublereal xmax;
    integer ipsv, jpsv;
    logical bswap;
    extern /* Subroutine */ int igraphdcopy_(integer *, doublereal *, integer *, 
	    doublereal *, integer *), igraphdswap_(integer *, doublereal *, integer 
	    *, doublereal *, integer *);
    logical xswap;
    extern doublereal igraphdlamch_(char *);
    extern integer igraphidamax_(integer *, doublereal *, integer *);
    doublereal smlnum;


/*  -- LAPACK auxiliary routine (version 3.4.2) --   
    -- LAPACK is a software package provided by Univ. of Tennessee,    --   
    -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--   
       September 2012   


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

       Parameter adjustments */
    tl_dim1 = *ldtl;
    tl_offset = 1 + tl_dim1;
    tl -= tl_offset;
    tr_dim1 = *ldtr;
    tr_offset = 1 + tr_dim1;
    tr -= tr_offset;
    b_dim1 = *ldb;
    b_offset = 1 + b_dim1;
    b -= b_offset;
    x_dim1 = *ldx;
    x_offset = 1 + x_dim1;
    x -= x_offset;

    /* Function Body   

       Do not check the input parameters for errors */

    *info = 0;

/*     Quick return if possible */

    if (*n1 == 0 || *n2 == 0) {
	return 0;
    }

/*     Set constants to control overflow */

    eps = igraphdlamch_("P");
    smlnum = igraphdlamch_("S") / eps;
    sgn = (doublereal) (*isgn);

    k = *n1 + *n1 + *n2 - 2;
    switch (k) {
	case 1:  goto L10;
	case 2:  goto L20;
	case 3:  goto L30;
	case 4:  goto L50;
    }

/*     1 by 1: TL11*X + SGN*X*TR11 = B11 */

L10:
    tau1 = tl[tl_dim1 + 1] + sgn * tr[tr_dim1 + 1];
    bet = abs(tau1);
    if (bet <= smlnum) {
	tau1 = smlnum;
	bet = smlnum;
	*info = 1;
    }

    *scale = 1.;
    gam = (d__1 = b[b_dim1 + 1], abs(d__1));
    if (smlnum * gam > bet) {
	*scale = 1. / gam;
    }

    x[x_dim1 + 1] = b[b_dim1 + 1] * *scale / tau1;
    *xnorm = (d__1 = x[x_dim1 + 1], abs(d__1));
    return 0;

/*     1 by 2:   
       TL11*[X11 X12] + ISGN*[X11 X12]*op[TR11 TR12]  = [B11 B12]   
                                         [TR21 TR22] */

L20:

/* Computing MAX   
   Computing MAX */
    d__7 = (d__1 = tl[tl_dim1 + 1], abs(d__1)), d__8 = (d__2 = tr[tr_dim1 + 1]
	    , abs(d__2)), d__7 = max(d__7,d__8), d__8 = (d__3 = tr[(tr_dim1 <<
	     1) + 1], abs(d__3)), d__7 = max(d__7,d__8), d__8 = (d__4 = tr[
	    tr_dim1 + 2], abs(d__4)), d__7 = max(d__7,d__8), d__8 = (d__5 = 
	    tr[(tr_dim1 << 1) + 2], abs(d__5));
    d__6 = eps * max(d__7,d__8);
    smin = max(d__6,smlnum);
    tmp[0] = tl[tl_dim1 + 1] + sgn * tr[tr_dim1 + 1];
    tmp[3] = tl[tl_dim1 + 1] + sgn * tr[(tr_dim1 << 1) + 2];
    if (*ltranr) {
	tmp[1] = sgn * tr[tr_dim1 + 2];
	tmp[2] = sgn * tr[(tr_dim1 << 1) + 1];
    } else {
	tmp[1] = sgn * tr[(tr_dim1 << 1) + 1];
	tmp[2] = sgn * tr[tr_dim1 + 2];
    }
    btmp[0] = b[b_dim1 + 1];
    btmp[1] = b[(b_dim1 << 1) + 1];
    goto L40;

/*     2 by 1:   
            op[TL11 TL12]*[X11] + ISGN* [X11]*TR11  = [B11]   
              [TL21 TL22] [X21]         [X21]         [B21] */

L30:
/* Computing MAX   
   Computing MAX */
    d__7 = (d__1 = tr[tr_dim1 + 1], abs(d__1)), d__8 = (d__2 = tl[tl_dim1 + 1]
	    , abs(d__2)), d__7 = max(d__7,d__8), d__8 = (d__3 = tl[(tl_dim1 <<
	     1) + 1], abs(d__3)), d__7 = max(d__7,d__8), d__8 = (d__4 = tl[
	    tl_dim1 + 2], abs(d__4)), d__7 = max(d__7,d__8), d__8 = (d__5 = 
	    tl[(tl_dim1 << 1) + 2], abs(d__5));
    d__6 = eps * max(d__7,d__8);
    smin = max(d__6,smlnum);
    tmp[0] = tl[tl_dim1 + 1] + sgn * tr[tr_dim1 + 1];
    tmp[3] = tl[(tl_dim1 << 1) + 2] + sgn * tr[tr_dim1 + 1];
    if (*ltranl) {
	tmp[1] = tl[(tl_dim1 << 1) + 1];
	tmp[2] = tl[tl_dim1 + 2];
    } else {
	tmp[1] = tl[tl_dim1 + 2];
	tmp[2] = tl[(tl_dim1 << 1) + 1];
    }
    btmp[0] = b[b_dim1 + 1];
    btmp[1] = b[b_dim1 + 2];
L40:

/*     Solve 2 by 2 system using complete pivoting.   
       Set pivots less than SMIN to SMIN. */

    ipiv = igraphidamax_(&c__4, tmp, &c__1);
    u11 = tmp[ipiv - 1];
    if (abs(u11) <= smin) {
	*info = 1;
	u11 = smin;
    }
    u12 = tmp[locu12[ipiv - 1] - 1];
    l21 = tmp[locl21[ipiv - 1] - 1] / u11;
    u22 = tmp[locu22[ipiv - 1] - 1] - u12 * l21;
    xswap = xswpiv[ipiv - 1];
    bswap = bswpiv[ipiv - 1];
    if (abs(u22) <= smin) {
	*info = 1;
	u22 = smin;
    }
    if (bswap) {
	temp = btmp[1];
	btmp[1] = btmp[0] - l21 * temp;
	btmp[0] = temp;
    } else {
	btmp[1] -= l21 * btmp[0];
    }
    *scale = 1.;
    if (smlnum * 2. * abs(btmp[1]) > abs(u22) || smlnum * 2. * abs(btmp[0]) > 
	    abs(u11)) {
/* Computing MAX */
	d__1 = abs(btmp[0]), d__2 = abs(btmp[1]);
	*scale = .5 / max(d__1,d__2);
	btmp[0] *= *scale;
	btmp[1] *= *scale;
    }
    x2[1] = btmp[1] / u22;
    x2[0] = btmp[0] / u11 - u12 / u11 * x2[1];
    if (xswap) {
	temp = x2[1];
	x2[1] = x2[0];
	x2[0] = temp;
    }
    x[x_dim1 + 1] = x2[0];
    if (*n1 == 1) {
	x[(x_dim1 << 1) + 1] = x2[1];
	*xnorm = (d__1 = x[x_dim1 + 1], abs(d__1)) + (d__2 = x[(x_dim1 << 1) 
		+ 1], abs(d__2));
    } else {
	x[x_dim1 + 2] = x2[1];
/* Computing MAX */
	d__3 = (d__1 = x[x_dim1 + 1], abs(d__1)), d__4 = (d__2 = x[x_dim1 + 2]
		, abs(d__2));
	*xnorm = max(d__3,d__4);
    }
    return 0;

/*     2 by 2:   
       op[TL11 TL12]*[X11 X12] +ISGN* [X11 X12]*op[TR11 TR12] = [B11 B12]   
         [TL21 TL22] [X21 X22]        [X21 X22]   [TR21 TR22]   [B21 B22]   

       Solve equivalent 4 by 4 system using complete pivoting.   
       Set pivots less than SMIN to SMIN. */

L50:
/* Computing MAX */
    d__5 = (d__1 = tr[tr_dim1 + 1], abs(d__1)), d__6 = (d__2 = tr[(tr_dim1 << 
	    1) + 1], abs(d__2)), d__5 = max(d__5,d__6), d__6 = (d__3 = tr[
	    tr_dim1 + 2], abs(d__3)), d__5 = max(d__5,d__6), d__6 = (d__4 = 
	    tr[(tr_dim1 << 1) + 2], abs(d__4));
    smin = max(d__5,d__6);
/* Computing MAX */
    d__5 = smin, d__6 = (d__1 = tl[tl_dim1 + 1], abs(d__1)), d__5 = max(d__5,
	    d__6), d__6 = (d__2 = tl[(tl_dim1 << 1) + 1], abs(d__2)), d__5 = 
	    max(d__5,d__6), d__6 = (d__3 = tl[tl_dim1 + 2], abs(d__3)), d__5 =
	     max(d__5,d__6), d__6 = (d__4 = tl[(tl_dim1 << 1) + 2], abs(d__4))
	    ;
    smin = max(d__5,d__6);
/* Computing MAX */
    d__1 = eps * smin;
    smin = max(d__1,smlnum);
    btmp[0] = 0.;
    igraphdcopy_(&c__16, btmp, &c__0, t16, &c__1);
    t16[0] = tl[tl_dim1 + 1] + sgn * tr[tr_dim1 + 1];
    t16[5] = tl[(tl_dim1 << 1) + 2] + sgn * tr[tr_dim1 + 1];
    t16[10] = tl[tl_dim1 + 1] + sgn * tr[(tr_dim1 << 1) + 2];
    t16[15] = tl[(tl_dim1 << 1) + 2] + sgn * tr[(tr_dim1 << 1) + 2];
    if (*ltranl) {
	t16[4] = tl[tl_dim1 + 2];
	t16[1] = tl[(tl_dim1 << 1) + 1];
	t16[14] = tl[tl_dim1 + 2];
	t16[11] = tl[(tl_dim1 << 1) + 1];
    } else {
	t16[4] = tl[(tl_dim1 << 1) + 1];
	t16[1] = tl[tl_dim1 + 2];
	t16[14] = tl[(tl_dim1 << 1) + 1];
	t16[11] = tl[tl_dim1 + 2];
    }
    if (*ltranr) {
	t16[8] = sgn * tr[(tr_dim1 << 1) + 1];
	t16[13] = sgn * tr[(tr_dim1 << 1) + 1];
	t16[2] = sgn * tr[tr_dim1 + 2];
	t16[7] = sgn * tr[tr_dim1 + 2];
    } else {
	t16[8] = sgn * tr[tr_dim1 + 2];
	t16[13] = sgn * tr[tr_dim1 + 2];
	t16[2] = sgn * tr[(tr_dim1 << 1) + 1];
	t16[7] = sgn * tr[(tr_dim1 << 1) + 1];
    }
    btmp[0] = b[b_dim1 + 1];
    btmp[1] = b[b_dim1 + 2];
    btmp[2] = b[(b_dim1 << 1) + 1];
    btmp[3] = b[(b_dim1 << 1) + 2];

/*     Perform elimination */

    for (i__ = 1; i__ <= 3; ++i__) {
	xmax = 0.;
	for (ip = i__; ip <= 4; ++ip) {
	    for (jp = i__; jp <= 4; ++jp) {
		if ((d__1 = t16[ip + (jp << 2) - 5], abs(d__1)) >= xmax) {
		    xmax = (d__1 = t16[ip + (jp << 2) - 5], abs(d__1));
		    ipsv = ip;
		    jpsv = jp;
		}
/* L60: */
	    }
/* L70: */
	}
	if (ipsv != i__) {
	    igraphdswap_(&c__4, &t16[ipsv - 1], &c__4, &t16[i__ - 1], &c__4);
	    temp = btmp[i__ - 1];
	    btmp[i__ - 1] = btmp[ipsv - 1];
	    btmp[ipsv - 1] = temp;
	}
	if (jpsv != i__) {
	    igraphdswap_(&c__4, &t16[(jpsv << 2) - 4], &c__1, &t16[(i__ << 2) - 4], 
		    &c__1);
	}
	jpiv[i__ - 1] = jpsv;
	if ((d__1 = t16[i__ + (i__ << 2) - 5], abs(d__1)) < smin) {
	    *info = 1;
	    t16[i__ + (i__ << 2) - 5] = smin;
	}
	for (j = i__ + 1; j <= 4; ++j) {
	    t16[j + (i__ << 2) - 5] /= t16[i__ + (i__ << 2) - 5];
	    btmp[j - 1] -= t16[j + (i__ << 2) - 5] * btmp[i__ - 1];
	    for (k = i__ + 1; k <= 4; ++k) {
		t16[j + (k << 2) - 5] -= t16[j + (i__ << 2) - 5] * t16[i__ + (
			k << 2) - 5];
/* L80: */
	    }
/* L90: */
	}
/* L100: */
    }
    if (abs(t16[15]) < smin) {
	t16[15] = smin;
    }
    *scale = 1.;
    if (smlnum * 8. * abs(btmp[0]) > abs(t16[0]) || smlnum * 8. * abs(btmp[1])
	     > abs(t16[5]) || smlnum * 8. * abs(btmp[2]) > abs(t16[10]) || 
	    smlnum * 8. * abs(btmp[3]) > abs(t16[15])) {
/* Computing MAX */
	d__1 = abs(btmp[0]), d__2 = abs(btmp[1]), d__1 = max(d__1,d__2), d__2 
		= abs(btmp[2]), d__1 = max(d__1,d__2), d__2 = abs(btmp[3]);
	*scale = .125 / max(d__1,d__2);
	btmp[0] *= *scale;
	btmp[1] *= *scale;
	btmp[2] *= *scale;
	btmp[3] *= *scale;
    }
    for (i__ = 1; i__ <= 4; ++i__) {
	k = 5 - i__;
	temp = 1. / t16[k + (k << 2) - 5];
	tmp[k - 1] = btmp[k - 1] * temp;
	for (j = k + 1; j <= 4; ++j) {
	    tmp[k - 1] -= temp * t16[k + (j << 2) - 5] * tmp[j - 1];
/* L110: */
	}
/* L120: */
    }
    for (i__ = 1; i__ <= 3; ++i__) {
	if (jpiv[4 - i__ - 1] != 4 - i__) {
	    temp = tmp[4 - i__ - 1];
	    tmp[4 - i__ - 1] = tmp[jpiv[4 - i__ - 1] - 1];
	    tmp[jpiv[4 - i__ - 1] - 1] = temp;
	}
/* L130: */
    }
    x[x_dim1 + 1] = tmp[0];
    x[x_dim1 + 2] = tmp[1];
    x[(x_dim1 << 1) + 1] = tmp[2];
    x[(x_dim1 << 1) + 2] = tmp[3];
/* Computing MAX */
    d__1 = abs(tmp[0]) + abs(tmp[2]), d__2 = abs(tmp[1]) + abs(tmp[3]);
    *xnorm = max(d__1,d__2);
    return 0;

/*     End of DLASY2 */

} /* igraphdlasy2_ */

