lammps/lib/linalg/dladiv.cpp

/* fortran/dladiv.f -- translated by f2c (version 20200916).
   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
*/

#ifdef __cplusplus
extern "C" {
#endif
#include "lmp_f2c.h"

/* > \brief \b DLADIV performs complex division in real arithmetic, avoiding unnecessary overflow. */

/*  =========== DOCUMENTATION =========== */

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

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

/*  Definition: */
/*  =========== */

/*       SUBROUTINE DLADIV( A, B, C, D, P, Q ) */

/*       .. Scalar Arguments .. */
/*       DOUBLE PRECISION   A, B, C, D, P, Q */
/*       .. */


/* > \par Purpose: */
/*  ============= */
/* > */
/* > \verbatim */
/* > */
/* > DLADIV performs complex division in  real arithmetic */
/* > */
/* >                       a + i*b */
/* >            p + i*q = --------- */
/* >                       c + i*d */
/* > */
/* > The algorithm is due to Michael Baudin and Robert L. Smith */
/* > and can be found in the paper */
/* > (char *)"A Robust Complex Division in Scilab" */
/* > \endverbatim */

/*  Arguments: */
/*  ========== */

/* > \param[in] A */
/* > \verbatim */
/* >          A is DOUBLE PRECISION */
/* > \endverbatim */
/* > */
/* > \param[in] B */
/* > \verbatim */
/* >          B is DOUBLE PRECISION */
/* > \endverbatim */
/* > */
/* > \param[in] C */
/* > \verbatim */
/* >          C is DOUBLE PRECISION */
/* > \endverbatim */
/* > */
/* > \param[in] D */
/* > \verbatim */
/* >          D is DOUBLE PRECISION */
/* >          The scalars a, b, c, and d in the above expression. */
/* > \endverbatim */
/* > */
/* > \param[out] P */
/* > \verbatim */
/* >          P is DOUBLE PRECISION */
/* > \endverbatim */
/* > */
/* > \param[out] Q */
/* > \verbatim */
/* >          Q is DOUBLE PRECISION */
/* >          The scalars p and q in the above expression. */
/* > \endverbatim */

/*  Authors: */
/*  ======== */

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

/* > \ingroup doubleOTHERauxiliary */

/*  ===================================================================== */
/* Subroutine */ int dladiv_(doublereal *a, doublereal *b, doublereal *c__,
        doublereal *d__, doublereal *p, doublereal *q)
{
    /* System generated locals */
    doublereal d__1, d__2;

    /* Local variables */
    doublereal s, aa, ab, bb, cc, cd, dd, be, un, ov, eps;
    extern doublereal dlamch_(char *, ftnlen);
    extern /* Subroutine */ int dladiv1_(doublereal *, doublereal *,
            doublereal *, doublereal *, doublereal *, doublereal *);


/*  -- 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 .. */
/*     .. */

/*  ===================================================================== */

/*     .. Parameters .. */

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

    aa = *a;
    bb = *b;
    cc = *c__;
    dd = *d__;
/* Computing MAX */
    d__1 = abs(*a), d__2 = abs(*b);
    ab = max(d__1,d__2);
/* Computing MAX */
    d__1 = abs(*c__), d__2 = abs(*d__);
    cd = max(d__1,d__2);
    s = 1.;
    ov = dlamch_((char *)"Overflow threshold", (ftnlen)18);
    un = dlamch_((char *)"Safe minimum", (ftnlen)12);
    eps = dlamch_((char *)"Epsilon", (ftnlen)7);
    be = 2. / (eps * eps);
    if (ab >= ov * .5) {
        aa *= .5;
        bb *= .5;
        s *= 2.;
    }
    if (cd >= ov * .5) {
        cc *= .5;
        dd *= .5;
        s *= .5;
    }
    if (ab <= un * 2. / eps) {
        aa *= be;
        bb *= be;
        s /= be;
    }
    if (cd <= un * 2. / eps) {
        cc *= be;
        dd *= be;
        s *= be;
    }
    if (abs(*d__) <= abs(*c__)) {
        dladiv1_(&aa, &bb, &cc, &dd, p, q);
    } else {
        dladiv1_(&bb, &aa, &dd, &cc, p, q);
        *q = -(*q);
    }
    *p *= s;
    *q *= s;

    return 0;

/*     End of DLADIV */

} /* dladiv_ */

/* > \ingroup doubleOTHERauxiliary */
/* Subroutine */ int dladiv1_(doublereal *a, doublereal *b, doublereal *c__,
        doublereal *d__, doublereal *p, doublereal *q)
{
    doublereal r__, t;
    extern doublereal dladiv2_(doublereal *, doublereal *, doublereal *,
            doublereal *, doublereal *, doublereal *);


/*  -- 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 .. */
/*     .. */

/*  ===================================================================== */

/*     .. Parameters .. */

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

    r__ = *d__ / *c__;
    t = 1. / (*c__ + *d__ * r__);
    *p = dladiv2_(a, b, c__, d__, &r__, &t);
    *a = -(*a);
    *q = dladiv2_(b, a, c__, d__, &r__, &t);

    return 0;

/*     End of DLADIV1 */

} /* dladiv1_ */

/* > \ingroup doubleOTHERauxiliary */
doublereal dladiv2_(doublereal *a, doublereal *b, doublereal *c__, doublereal
        *d__, doublereal *r__, doublereal *t)
{
    /* System generated locals */
    doublereal ret_val;

    /* Local variables */
    doublereal br;


/*  -- 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 .. */
/*     .. */

/*  ===================================================================== */

/*     .. Parameters .. */

/*     .. Local Scalars .. */
/*     .. */
/*     .. Executable Statements .. */

    if (*r__ != 0.) {
        br = *b * *r__;
        if (br != 0.) {
            ret_val = (*a + br) * *t;
        } else {
            ret_val = *a * *t + *b * *t * *r__;
        }
    } else {
        ret_val = (*a + *d__ * (*b / *c__)) * *t;
    }

    return ret_val;

/*     End of DLADIV2 */

} /* dladiv2_ */

#ifdef __cplusplus
        }
#endif