strot_diff_equil.C

/*
 *  Function Star_rot_diff::equilibrium
 *
 *    (see file star_rot_diff.h for documentation).
 *
 */

/*
 *   Copyright (c) 2025 Santiago Jaraba
 *
 *   This file is part of LORENE.
 *
 *   LORENE is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License version 2
 *   as published by the Free Software Foundation.
 *
 *   LORENE is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with LORENE; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

// C headers
#include <cmath>

// Lorene headers
#include "star_rot_diff.h"
#include "param.h"
#include "graphique.h"
#include "utilitaires.h"
#include "unites.h"

#include "tenseur.h" // Unavoidable for now due to Poisson-solving functions


namespace Lorene{
void Star_rot_diff::equilibrium(double ent_c, double omega_c0, double fact_omega, 
                int nzadapt, const Tbl& ent_limit, 
                const Itbl& icontrol,
                const Tbl& control, double mbar_wanted, 
                double aexp_mass, Tbl& diff, Param*){

    // Fundamental constants and units
    // --------------------------------
    using namespace Unites ;

    // For the display 
    // ---------------
    char display_bold[]="x[1m" ; display_bold[0] = 27 ;
    char display_normal[] = "x[0m" ; display_normal[0] = 27 ;


    // Grid parameters
    // ----------------

    const Mg3d* mg = mp.get_mg() ;
    int nz = mg->get_nzone() ;    // total number of domains
    int nzm1 = nz - 1 ;

    // The following is required to initialize mp_prev as a Map_et:
    Map_et& mp_et = dynamic_cast<Map_et&>(mp) ; 

    // Index of the point at phi=0, theta=pi/2 at the surface of the star:
    assert(mg->get_type_t() == SYM) ; 
    int l_b = nzet - 1 ; 
    int i_b = mg->get_nr(l_b) - 1 ; 
    int j_b = mg->get_nt(l_b) - 1 ; 
    int k_b = 0 ; 
    
    // Value of the enthalpy defining the surface of the star
    double ent_b = ent_limit(nzet-1) ;
    
    // Parameters to control the iteration
    // -----------------------------------
    
    int mer_max = icontrol(0) ; 
    int mer_rot = icontrol(1) ;
    int mer_change_omega = icontrol(2) ; 
    int mer_fix_omega = icontrol(3) ; 
    int mer_mass = icontrol(4) ; 
    int mermax_poisson = icontrol(5) ; 
    int mer_triax = icontrol(6) ; 
    int delta_mer_kep = icontrol(7) ;  

    // Protections:
    if (mer_change_omega < mer_rot) {
    cout << "Star_rot_diff::equilibrium: mer_change_omega < mer_rot !" << endl ;
    cout << " mer_change_omega = " << mer_change_omega << endl ; 
    cout << " mer_rot = " << mer_rot << endl ; 
    abort() ; 
    }
    if (mer_fix_omega < mer_change_omega) {
    cout << "Star_rot_diff::equilibrium: mer_fix_omega < mer_change_omega !" 
         << endl ;
    cout << " mer_fix_omega = " << mer_fix_omega << endl ; 
    cout << " mer_change_omega = " << mer_change_omega << endl ; 
    abort() ; 
    }

    // In order to converge to a given baryon mass, shall the central
    // enthalpy be varied or Omega ?
    bool change_ent = true ; 
    if (mer_mass < 0) {
        change_ent = false ; 
        mer_mass = abs(mer_mass) ;
    }
    
    double precis = control(0) ; 
    double omega_ini = control(1) ; 
    double relax = control(2) ;
    double relax_prev = double(1) - relax ;  
    double relax_poisson = control(3) ; 
    double thres_adapt = control(4) ; 
    double ampli_triax = control(5) ; 
    double precis_adapt = control(6) ; 


    // Error indicators
    // ----------------
    
    diff.set_etat_qcq() ; 
    double& diff_ent = diff.set(0) ; 
    double& diff_nuf = diff.set(1) ; 
    double& diff_nuq = diff.set(2) ; 
//    double& diff_dzeta = diff.set(3) ; 
//    double& diff_ggg = diff.set(4) ; 
    double& diff_shift_x = diff.set(5) ; 
    double& diff_shift_y = diff.set(6) ; 
    double& vit_triax = diff.set(7) ; 

    // Parameters for the function Map_et::adapt
    // -----------------------------------------
    
    Param par_adapt ; 
    int nitermax = 100 ;  
    int niter ; 
    int adapt_flag = 1 ;    //  1 = performs the full computation, 
                //  0 = performs only the rescaling by 
                //      the factor alpha_r
    int nz_search = nzet + 1 ;  // Number of domains for searching the enthalpy
                //  isosurfaces
    double alpha_r ; 
    double reg_map = 1. ; // 1 = regular mapping, 0 = contracting mapping

    par_adapt.add_int(nitermax, 0) ; // maximum number of iterations to
                     // locate zeros by the secant method
    par_adapt.add_int(nzadapt, 1) ; // number of domains where the adjustment 
                    // to the isosurfaces of ent is to be 
                    // performed
    par_adapt.add_int(nz_search, 2) ;   // number of domains to search for
                    // the enthalpy isosurface
    par_adapt.add_int(adapt_flag, 3) ; //  1 = performs the full computation, 
                       //  0 = performs only the rescaling by 
                       //      the factor alpha_r
    par_adapt.add_int(j_b, 4) ; //  theta index of the collocation point 
                    //  (theta_*, phi_*)
    par_adapt.add_int(k_b, 5) ; //  theta index of the collocation point 
                    //  (theta_*, phi_*)

    par_adapt.add_int_mod(niter, 0) ;  //  number of iterations actually used in 
                       //  the secant method
    
    par_adapt.add_double(precis_adapt, 0) ; // required absolute precision in 
                         // the determination of zeros by 
                         // the secant method
    par_adapt.add_double(reg_map, 1)    ;  // 1. = regular mapping, 0 = contracting mapping
    
    par_adapt.add_double(alpha_r, 2) ;  // factor by which all the radial 
                       // distances will be multiplied 
           
    par_adapt.add_tbl(ent_limit, 0) ;   // array of values of the field ent 
                        // to define the isosurfaces.              

    // Parameters for the function Map_et::poisson for nuf
    // ----------------------------------------------------

    double precis_poisson = 1.e-16 ;  

    Cmp cssjm1_tggg(ssjm1_tggg) ;
    Cmp cssjm1_khi(ssjm1_khi) ; 
    Tenseur cssjm1_wshift(mp, 1, CON, mp.get_bvect_cart() ) ;
    cssjm1_wshift.set_etat_qcq() ;
    for (int i=1; i<=3; i++) {
    cssjm1_wshift.set(i-1) = ssjm1_wshift(i) ; 
    }
    
    Tenseur cshift(mp, 1, CON, mp.get_bvect_cart() ) ;
    cshift.set_etat_qcq() ;
    for (int i=1; i<=3; i++) {
      cshift.set(i-1) = -beta(i) ; 
    }

    Tenseur cw_shift(mp, 1, CON, mp.get_bvect_cart() ) ;
    cw_shift.set_etat_qcq() ;
    for (int i=1; i<=3; i++) {
      cw_shift.set(i-1) = w_shift(i) ; 
    }

    Tenseur ckhi_shift(mp) ;
    ckhi_shift.set_etat_qcq() ;
    ckhi_shift.set() = khi_shift ; 

    Param par_poisson_nuf ; 
    par_poisson_nuf.add_int(mermax_poisson,  0) ;  // maximum number of iterations
    par_poisson_nuf.add_double(relax_poisson,  0) ; // relaxation parameter
    par_poisson_nuf.add_double(precis_poisson, 1) ; // required precision
    par_poisson_nuf.add_int_mod(niter, 0) ;  //  number of iterations actually used 
    par_poisson_nuf.add_scalar_mod( ssjm1_nuf ) ; 
                       
    Param par_poisson_nuq ; 
    par_poisson_nuq.add_int(mermax_poisson,  0) ;  // maximum number of iterations
    par_poisson_nuq.add_double(relax_poisson,  0) ; // relaxation parameter
    par_poisson_nuq.add_double(precis_poisson, 1) ; // required precision
    par_poisson_nuq.add_int_mod(niter, 0) ;  //  number of iterations actually used 
    par_poisson_nuq.add_scalar_mod( ssjm1_nuq ) ; 
                       
    Param par_poisson_tggg ; 
    par_poisson_tggg.add_int(mermax_poisson,  0) ;  // maximum number of iterations
    par_poisson_tggg.add_double(relax_poisson,  0) ; // relaxation parameter
    par_poisson_tggg.add_double(precis_poisson, 1) ; // required precision
    par_poisson_tggg.add_int_mod(niter, 0) ;  //  number of iterations actually used 
    par_poisson_tggg.add_cmp_mod( cssjm1_tggg ) ; 
    double lambda_tggg ;
    par_poisson_tggg.add_double_mod( lambda_tggg ) ; 
    
    Param par_poisson_dzeta ; 
    double lbda_grv2 ;
    par_poisson_dzeta.add_double_mod( lbda_grv2 ) ; 
                       
    // Parameters for the function Scalar::poisson_vect
    // -------------------------------------------------

    Param par_poisson_vect ; 

    par_poisson_vect.add_int(mermax_poisson,  0) ;  // maximum number of iterations
    par_poisson_vect.add_double(relax_poisson,  0) ; // relaxation parameter
    par_poisson_vect.add_double(precis_poisson, 1) ; // required precision
    par_poisson_vect.add_cmp_mod( cssjm1_khi ) ; 
    par_poisson_vect.add_tenseur_mod( cssjm1_wshift ) ; 
    par_poisson_vect.add_int_mod(niter, 0) ;  


    // Initializations
    // ---------------

    // Initial angular velocities 
    double omega_c = 0 ;
    
    double accrois_omega = (omega_c0 - omega_ini) / 
                double(mer_fix_omega - mer_change_omega) ; 
 

    update_metric() ;    //update of the metric quantities 

    equation_of_state() ;  // update of the density, pressure,...etc

    hydro_euler() ; //update of the hydro quantities relative to the 
                    //  Eulerian observer

    // Quantities at the previous step :
    Map_et mp_prev = mp_et ;
    Scalar ent_prev = ent ;
    Scalar logn_prev = logn ;
    Scalar dzeta_prev = dzeta ;

    // Creation of uninitialized tensors:
    Scalar source_nuf(mp) ;    // source term in the equation for nuf
    Scalar source_nuq(mp) ;    // source term in the equation for nuq
    Scalar source_dzf(mp) ; // matter source term in the eq. for dzeta
    Scalar source_dzq(mp) ; // quadratic source term in the eq. for dzeta
    Scalar source_tggg(mp) ;    // source term in the eq. for tggg
    Vector source_shift(mp, CON, mp.get_bvect_cart()) ;  // source term for shift
    Scalar mlngamma(mp) ;   // centrifugal potential
    
    // Preparations for the Poisson equations:
    // --------------------------------------
    if (nuf.get_etat() == ETATZERO) {
    nuf.set_etat_qcq() ; 
    nuf = 0 ; 
    }
    
    if (relativistic) {
    if (nuq.get_etat() == ETATZERO) {
        nuq.set_etat_qcq() ; 
        nuq = 0 ; 
    }

    if (tggg.get_etat() == ETATZERO) {
        tggg.set_etat_qcq() ; 
        tggg = 0 ; 
    }
    
    if (dzeta.get_etat() == ETATZERO) {
        dzeta.set_etat_qcq() ; 
        dzeta = 0 ; 
    }
    }

    // Output files
    // -------------

    ofstream fichconv("convergence.d") ;    // Output file for diff_ent
    fichconv << "#     diff_ent    GRV2    max_triax   vit_triax" << endl ;   

    ofstream fichfreq("frequency.d") ;    // Output file for  omega
    fichfreq << "#       f [Hz]" << endl ; 

    ofstream fichevol("evolution.d") ;    // Output file for various quantities
    fichevol << 
        "#       |dH/dr_eq/dH/dr_pole|      r_pole/r_eq ent_c" 
        << endl ; 

    diff_ent = 1 ;
    double err_grv2 = 1 ;
    double max_triax_prev = 0 ;     // Triaxial amplitude at previous step

    //=========================================================================
    //          Start of iteration
    //=========================================================================

    for(int mer=0 ; (diff_ent > precis) && (mer<mer_max) ; mer++ ) {

    cout << "-----------------------------------------------" << endl ;
    cout << "step: " << mer << endl ;
    cout << "diff_ent = " << display_bold << diff_ent << display_normal
        << endl ;    
    cout << "err_grv2 = " << err_grv2 << endl ;    
    fichconv << mer ;
    fichfreq << mer ;
    fichevol << mer ;

    // Switch on rotation    
    if (mer >= mer_rot) {
    
        if (mer < mer_change_omega) {
        omega_c = omega_ini ; 
        }
        else {
        if (mer <= mer_fix_omega) {
            omega_c = omega_ini + accrois_omega * 
                    (mer - mer_change_omega) ;
        }
        }

    }

    //-----------------------------------------------
    //  Sources of the Poisson equations
    //-----------------------------------------------
    
    // Source for nu
    // -------------
    Scalar bet = log(bbb) ; 
    bet.std_spectral_base() ;

    Vector d_logn = logn.derive_cov( mp.flat_met_spher() ) ; 
    Vector d_bet = bet.derive_cov( mp.flat_met_spher() ) ; 

    if (relativistic) {
        source_nuf =  qpig * a_car *( ener_euler + s_euler ) ; 

        source_nuq = ak_car - d_logn(1)*(d_logn(1)+d_bet(1))
        - d_logn(2)*(d_logn(2)+d_bet(2))
        - d_logn(3)*(d_logn(3)+d_bet(3)) ; 
    }
    else {
        source_nuf = qpig * nbar ; 

        source_nuq = 0 ; 
    }
    source_nuf.std_spectral_base() ;    
    source_nuq.std_spectral_base() ; 

    // Source for dzeta
    // ----------------
    source_dzf = 2 * qpig * a_car * (press + (ener_euler+press) * uuu*uuu ) ;
    source_dzf.std_spectral_base() ; 
  
    source_dzq = 1.5 * ak_car 
        - d_logn(1)*d_logn(1) - d_logn(2)*d_logn(2) - d_logn(3)*d_logn(3) ;         
    source_dzq.std_spectral_base() ; 
    
    // Source for tggg
    // ---------------
    
    source_tggg = 4 * qpig * nn * a_car * bbb * press ;
    source_tggg.std_spectral_base() ; 
    
    source_tggg.mult_rsint() ; 
    

    // Source for shift
    // ----------------
        
    // Matter term: 
    source_shift = (-4*qpig) * nn * a_car  * (ener_euler + press)
                * u_euler ;

    // Quadratic terms:
    Vector vtmp =  6 * bet.derive_con( mp.flat_met_spher() ) 
        - 2 * logn.derive_con( mp.flat_met_spher() ) ;
    vtmp.change_triad(mp.get_bvect_cart()) ; 

    Vector squad  = nn * contract(tkij, 1, vtmp, 0) ; 

    source_shift = source_shift + squad.up(0, mp.flat_met_cart() ) ;    

    //----------------------------------------------
    // Resolution of the Poisson equation for nuf 
    //----------------------------------------------

    source_nuf.poisson(par_poisson_nuf, nuf) ; 
    
    cout << "Test of the Poisson equation for nuf :" << endl ; 
    Tbl err = source_nuf.test_poisson(nuf, cout, true) ; 
    diff_nuf = err(0, 0) ; 
    
    //---------------------------------------
    // Triaxial perturbation of nuf
    //---------------------------------------
    
    if (mer == mer_triax) {
    
        if ( mg->get_np(0) == 1 ) {
        cout << 
        "Star_rot_diff::equilibrium: np must be stricly greater than 1"
        << endl << " to set a triaxial perturbation !" << endl ; 
        abort() ; 
        }
    
        const Coord& phi = mp.phi ; 
        const Coord& sint = mp.sint ; 
        Scalar perturb(mp) ; 
        perturb = 1 + ampli_triax * sint*sint * cos(2*phi) ;
        nuf = nuf * perturb ;  
        
        nuf.std_spectral_base() ;    // set the bases for spectral expansions
                    //  to be the standard ones for a 
                    //  scalar field

    }
    
    // Monitoring of the triaxial perturbation
    // ---------------------------------------
    
    const Valeur& va_nuf = nuf.get_spectral_va() ;
    va_nuf.coef() ;     // Computes the spectral coefficients
    double max_triax = 0 ; 

    if ( mg->get_np(0) > 1 ) {

        for (int l=0; l<nz; l++) {  // loop on the domains
        for (int j=0; j<mg->get_nt(l); j++) {
            for (int i=0; i<mg->get_nr(l); i++) {
        
            // Coefficient of cos(2 phi) : 
            double xcos2p = (*(va_nuf.c_cf))(l, 2, j, i) ; 

            // Coefficient of sin(2 phi) : 
            double xsin2p = (*(va_nuf.c_cf))(l, 3, j, i) ; 
            
            double xx = sqrt( xcos2p*xcos2p + xsin2p*xsin2p ) ; 
            
            max_triax = ( xx > max_triax ) ? xx : max_triax ;           
            }
        } 
        }
        
    }
    
    cout << "Triaxial part of nuf : " << max_triax << endl ;

    if (relativistic) {
        
        //----------------------------------------------
        // Resolution of the Poisson equation for nuq 
        //----------------------------------------------

        source_nuq.poisson(par_poisson_nuq, nuq) ; 
        
        cout << "Test of the Poisson equation for nuq :" << endl ; 
        err = source_nuq.test_poisson(nuq, cout, true) ;
        diff_nuq = err(0, 0) ; 
    
        //---------------------------------------------------------
        // Resolution of the vector Poisson equation for the shift
        //---------------------------------------------------------

        for (int i=1; i<=3; i++) {
            if(source_shift(i).get_etat() != ETATZERO) {
              if(source_shift(i).dz_nonzero()) {
              assert( source_shift(i).get_dzpuis() == 4 ) ; 
              }
              else{
              (source_shift.set(i)).set_dzpuis(4) ; 
              }
          }
        }

        double lambda_shift = double(1) / double(3) ; 

        if ( mg->get_np(0) == 1 ) {
        lambda_shift = 0 ; 
        }
        
        Tenseur csource_shift(mp, 1, CON, mp.get_bvect_cart() ) ;
        csource_shift.set_etat_qcq() ;
        if ( (source_shift(1).get_etat() == ETATZERO) &&
        (source_shift(2).get_etat() == ETATZERO) &&
        (source_shift(3).get_etat() == ETATZERO) ) {
            csource_shift.set_etat_zero() ;
        } 
        else {
            csource_shift.set_etat_qcq() ;
        for (int i=1; i<=3; i++) {
            csource_shift.set(i-1) = source_shift(i) ; 
            }
            csource_shift.set(2).set_etat_zero() ;
        }
        
        csource_shift.poisson_vect(lambda_shift, par_poisson_vect, 
                          cshift, cw_shift, ckhi_shift) ;  
        // beta = -source_shift.poisson(lambda_shift, par_poisson_vect, 2) ;

        for (int i=1; i<=3; i++) {
        beta.set(i) = - cshift(i-1) ;
        w_shift.set(i) = cw_shift(i-1) ; 
        }
        khi_shift = ckhi_shift() ;        
        
        cout << "Test of the Poisson equation for shift_x :" << endl ; 
        err = source_shift(1).test_poisson(-beta(1), cout, true) ;
        diff_shift_x = err(0, 0) ; 
    
        cout << "Test of the Poisson equation for shift_y :" << endl ; 
        err = source_shift(2).test_poisson(-beta(2), cout, true) ;
        diff_shift_y = err(0, 0) ; 
        
        // Computation of tnphi and nphi from the Cartesian components
        //  of the shift
        // -----------------------------------------------------------
        
        fait_nphi() ; 
    
    }

    //-----------------------------------------
    // Determination of the fluid velociy U
    //-----------------------------------------
    
    if (mer > mer_fix_omega + delta_mer_kep) {
        
            omega_c *= fact_omega ;  // Increase of the angular velocity if 
    }              //  fact_omega != 1
    
    
    bool omega_trop_grand = false ; 
    bool kepler = true ; 

    while ( kepler ) {
    
        // Possible decrease of Omega to ensure a velocity < c 
    
        bool superlum = true ; 
    
        while ( superlum ) {
    
        // Computation of Omega(r,theta)

        if (omega_c == 0.) {
            omega_field = 0 ; 
        }
        else if (par_frot.get_taille() == 5) { // Uryu rotation profile
            // First, compute F_e and F_max
            Scalar brst2 = bbb ;
            brst2.annule_domain(nzm1) ; 
            brst2.std_spectral_base() ;
            brst2.mult_rsint() ;        //  Multiplication by r sin(theta)
            brst2 = brst2*brst2 ;        
            Scalar nnn2 = nn * nn ;

            double omnp = omega_field.val_grid_point(l_b, k_b, j_b, i_b) - nphi.val_grid_point(l_b, k_b, j_b, i_b) ;
            double F_e = brst2.val_grid_point(l_b, k_b, j_b, i_b) * omnp /
            ( nnn2.val_grid_point(l_b, k_b, j_b, i_b) - 
            brst2.val_grid_point(l_b, k_b, j_b, i_b) * omnp * omnp ) ;

            if (F_e == double(0)) {} // Initial iteration
            else {
                int l, k, j, i ;
                double om_max = 0 ;
                double om_lkji, F_max ;
                for (l=0; l<nzet+1; l++) {
                for (k=0; k<mg->get_np(l); k++) {
                    for (j=0; j<mg->get_nt(l); j++) {
                    for (i=0; i<mg->get_nr(l); i++) {
                        om_lkji = omega_field.val_grid_point(l, k, j, i) ;
                        if (om_lkji > om_max) {
                            om_max = om_lkji ;
                            omnp = om_max - nphi.val_grid_point(l, k, j, i) ;
                            F_max = brst2.val_grid_point(l, k, j, i) * omnp /
                            ( nnn2.val_grid_point(l, k, j, i) - 
                            brst2.val_grid_point(l, k, j, i) * omnp * omnp ) ;
                        }
                    }
                    }
                }
                }

                // Now A^2 and B^2, parameters for omega_frot, can be computed
                double lambda1 = par_frot(1) ;
                double lambda2 = par_frot(2) ;
                int p = 1 ;
                int q = 3 ;
                par_frot.set(3) = pow(pow(F_e*F_max,p)/pow(omega_c, p+q) * (lambda2*pow(F_e, q)-lambda1*pow(F_max, q) )
                                / ((lambda1-1)*pow(F_e, p) - (lambda2-1)*pow(F_max, p)), 1./(p+q) ) ;
                par_frot.set(4) = F_e*F_max/omega_c * pow((lambda2*pow(F_e, q)-lambda1*pow(F_max, q))
                                / (lambda2*(lambda1-1)*pow(F_e, p+q) - lambda1*(lambda2-1)*pow(F_max, p+q)), 1./p) ;

                cout << F_e << " " << F_max << endl ;
            }

            par_frot.set(0) = omega_c ;

            cout << "Parameters of Omega(F) : " << par_frot << endl ; 
            
            double omeg_min = 0 ;
            double omeg_max = par_frot(1) * omega_c ;
            double precis1 = 1.e-14 ;
            int nitermax1 = 100 ; 

            fait_omega_field(omeg_min, omeg_max, precis1, nitermax1) ;
        }
        else { // Usual rotation profile
            par_frot.set(0) = omega_c ; 
            if (par_frot(2) != double(0)) {  // fixed a = R_eq / R_0
            par_frot.set(1) = ray_eq() / par_frot(2) ; 
            }
            double omeg_min = 0 ; 
            double omeg_max = omega_c ;
            double precis1 = 1.e-14 ;
            int nitermax1 = 100 ; 

            fait_omega_field(omeg_min, omeg_max, precis1, nitermax1) ;
        }

        // New fluid velocity U :
    
        Scalar tmp = omega_field - nphi ; 
        tmp.annule_domain(nzm1) ; 
        tmp.std_spectral_base() ;
    
        tmp.mult_rsint() ;      //  Multiplication by r sin(theta)

        uuu = bbb / nn * tmp ; 
    
        if (uuu.get_etat() == ETATQCQ) {
            // Same basis as (Omega -N^phi) r sin(theta) :
            (uuu.set_spectral_va()).set_base( tmp.get_spectral_va().get_base() ) ;   
        }

        // Is the new velocity larger than c in the equatorial plane ?
    
        superlum = false ; 
    
        for (int l=0; l<nzet; l++) {
            for (int i=0; i<mg->get_nr(l); i++) {
        
            double u1 = uuu.val_grid_point(l, 0, j_b, i) ; 
            if (u1 >= 1.) {     // superluminal velocity
                superlum = true ; 
                cout << "U > c  for l, i : " << l << "  " << i 
                 << "   U = " << u1 << endl ;  
            }
            }
        }
        if ( superlum ) {
            cout << "**** VELOCITY OF LIGHT REACHED ****" << endl ; 
            omega_c /= fact_omega ;    // Decrease of Omega_c
            cout << "New central rotation frequency : " 
             << omega/(2.*M_PI) * f_unit <<  " Hz" << endl ; 
            omega_trop_grand = true ;  
        }
        }   // end of while ( superlum )

    
        // New computation of U (which this time is not superluminal)
        //  as well as of gam_euler, ener_euler, etc...
        // -----------------------------------

        hydro_euler() ; 
    

        //------------------------------------------------------
        //  First integral of motion 
        //------------------------------------------------------
    
        // Centrifugal potential : 
        if (relativistic) {
        mlngamma = - log( gam_euler ) ;
        }
        else {
        mlngamma = - 0.5 * uuu*uuu ; 
        }
    
        // Equatorial values of various potentials :
        double nuf_b  = nuf.val_grid_point(l_b, k_b, j_b, i_b) ; 
        double nuq_b  = nuq.val_grid_point(l_b, k_b, j_b, i_b) ; 
        double mlngamma_b  = mlngamma.val_grid_point(l_b, k_b, j_b, i_b) ; 
        double primf_b = prim_field.val_grid_point(l_b, k_b, j_b, i_b) ;
        
        
        // Central values of various potentials :
        double nuf_c = nuf.val_grid_point(0,0,0,0) ; 
        double nuq_c = nuq.val_grid_point(0,0,0,0) ; 
        double mlngamma_c = 0 ;
        double primf_c = prim_field.val_grid_point(0,0,0,0) ; 
    
        // Scale factor to ensure that the enthalpy is equal to ent_b at 
        //  the equator
        double alpha_r2 = ( ent_c - ent_b + mlngamma_c - mlngamma_b
                + nuq_c - nuq_b + primf_c - primf_b) 
                / ( nuf_b - nuf_c  ) ;
        alpha_r = sqrt(alpha_r2) ;
        cout << "alpha_r = " << alpha_r << endl ; 

        // Readjustment of nu :
        // -------------------

        logn = alpha_r2 * nuf + nuq ;
        double nu_c =  logn.val_grid_point(0,0,0,0) ;

        // First integral   --> enthalpy in all space
        //-----------------

        ent = (ent_c + nu_c + mlngamma_c) - logn - mlngamma - prim_field ;

        // Test: is the enthalpy negative somewhere in the equatorial plane
        //  inside the star ? If yes, this means that the Keplerian velocity
        //  has been overstep.

        kepler = false ; 
        for (int l=0; l<nzet; l++) {
        int imax = mg->get_nr(l) - 1 ;
        if (l == l_b) imax-- ;  // The surface point is skipped
        for (int i=0; i<imax; i++) { 
            if ( ent.val_grid_point(l, 0, j_b, i) < 0. ) {
            kepler = true ;
            cout << "ent < 0 for l, i : " << l << "  " << i 
                 << "   ent = " << ent.val_grid_point(l, 0, j_b, i) << endl ;  
            } 
        }
        }
    
        if ( kepler ) {
        cout << "**** KEPLERIAN VELOCITY REACHED ****" << endl ; 
        omega_c /= fact_omega ;    // Omega is decreased
        cout << "New central rotation frequency : " 
             << omega_c/(2.*M_PI) * f_unit << " Hz" << endl ; 
        omega_trop_grand = true ;  
        }

    }   // End of while ( kepler )
    
    if ( omega_trop_grand ) {   // fact_omega is decreased for the
                    //  next step 
        fact_omega = sqrt( fact_omega ) ; 
        cout << "**** New fact_omega : " << fact_omega << endl ; 
    }

    //----------------------------------------------------
    // Adaptation of the mapping to the new enthalpy field
    //----------------------------------------------------
    
    // Shall the adaptation be performed (cusp) ?
    // ------------------------------------------
    
    double dent_eq = ent.dsdr().val_grid_point(l_b, k_b, j_b, i_b) ; 
    double dent_pole = ent.dsdr().val_grid_point(l_b, k_b, 0, i_b) ;
    double rap_dent = fabs( dent_eq / dent_pole ) ; 
    cout << "| dH/dr_eq / dH/dr_pole | = " << rap_dent << endl ; 
    
    if ( rap_dent < thres_adapt ) {
        adapt_flag = 0 ;    // No adaptation of the mapping 
        cout << "******* FROZEN MAPPING  *********" << endl ; 
    }
    else{
        adapt_flag = 1 ;    // The adaptation of the mapping is to be
                //  performed
    }

    mp_prev = mp_et ; 

    Cmp cent(ent) ; 
    mp.adapt(cent, par_adapt) ; 

    //----------------------------------------------------
    // Computation of the enthalpy at the new grid points
    //----------------------------------------------------
    
    mp_prev.homothetie(alpha_r) ; 
    
    mp.reevaluate(&mp_prev, nzet+1, cent) ;
    ent = cent ; 

    //----------------------------------------------------
    // Equation of state  
    //----------------------------------------------------
    
    equation_of_state() ;   // computes new values for nbar (n), ener (e) 
                // and press (p) from the new ent (H)
    
    //---------------------------------------------------------
    // Matter source terms in the gravitational field equations 
    //---------------------------------------------------------

    //## Computation of tnphi and nphi from the Cartesian components
    //  of the shift for the test in hydro_euler():
        
        fait_nphi() ; 

    hydro_euler() ;     // computes new values for ener_euler (E), 
                // s_euler (S) and u_euler (U^i)

    if (relativistic) {

        //-------------------------------------------------------
        //  2-D Poisson equation for tggg
        //-------------------------------------------------------
        
        Cmp csource_tggg(source_tggg) ;
        Cmp ctggg(tggg) ; 
        mp.poisson2d(csource_tggg, mp.cmp_zero(), par_poisson_tggg,
             ctggg) ; 
        tggg = ctggg ;

        
        //-------------------------------------------------------
        //  2-D Poisson equation for dzeta
        //-------------------------------------------------------
        
        Cmp csource_dzf(source_dzf) ; 
        Cmp csource_dzq(source_dzq) ; 
        Cmp cdzeta(dzeta) ; 
        mp.poisson2d(csource_dzf, csource_dzq, par_poisson_dzeta,
             cdzeta) ; 
        dzeta = cdzeta ;
        
        err_grv2 = lbda_grv2 - 1; 
        cout << "GRV2: " << err_grv2 << endl ; 
        
    }
    else {
        err_grv2 = grv2() ; 
    }


    //---------------------------------------
    // Computation of the metric coefficients (except for N^phi)
    //---------------------------------------

    // Relaxations on nu and dzeta :  

    if (mer >= 10) {
        logn = relax * logn + relax_prev * logn_prev ;

        dzeta = relax * dzeta + relax_prev * dzeta_prev ; 
    }
    
    // Update of the metric coefficients N, A, B and computation of K_ij :

    update_metric() ; 
    
    //-----------------------
    //  Informations display
    //-----------------------

    partial_display(cout) ; 
    fichfreq << "  " << omega_c / (2*M_PI) * f_unit ; 
    fichevol << "  " << rap_dent ; 
    fichevol << "  " << ray_pole() / ray_eq() ; 
    fichevol << "  " << ent_c ; 

    //-----------------------------------------
    // Convergence towards a given baryon mass 
    //-----------------------------------------

    if (mer > mer_mass) {
        
        double xx ; 
        if (mbar_wanted > 0.) {
        xx = mass_b() / mbar_wanted - 1. ;
        cout << "Discrep. baryon mass <-> wanted bar. mass : " << xx 
             << endl ; 
        }
        else{
        xx = mass_g() / fabs(mbar_wanted) - 1. ;
        cout << "Discrep. grav. mass <-> wanted grav. mass : " << xx 
             << endl ; 
        }
        double xprog = ( mer > 2*mer_mass) ? 1. : 
                 double(mer-mer_mass)/double(mer_mass) ; 
        xx *= xprog ; 
        double ax = .5 * ( 2. + xx ) / (1. + xx ) ; 
        double fact = pow(ax, aexp_mass) ; 
        cout << "  xprog, xx, ax, fact : " << xprog << "  " <<
            xx << "  " << ax << "  " << fact << endl ; 

        if ( change_ent ) {
        ent_c *= fact ; 
        }
        else {
        if (mer%4 == 0) omega_c *= fact ; 
        }
    }
    

    //------------------------------------------------------------
    //  Relative change in enthalpy with respect to previous step 
    //------------------------------------------------------------

    Tbl diff_ent_tbl = diffrel( ent, ent_prev ) ; 
    diff_ent = diff_ent_tbl(0) ; 
    for (int l=1; l<nzet; l++) {
        diff_ent += diff_ent_tbl(l) ; 
    }
    diff_ent /= nzet ; 
    
    fichconv << "  " << log10( fabs(diff_ent) + 1.e-16 ) ;
    fichconv << "  " << log10( fabs(err_grv2) + 1.e-16 ) ;
    fichconv << "  " << log10( fabs(max_triax) + 1.e-16 ) ;

    vit_triax = 0 ;
    if ( (mer > mer_triax+1) && (max_triax_prev > 1e-13) ) {
        vit_triax = (max_triax - max_triax_prev) / max_triax_prev ; 
    }

    fichconv << "  " << vit_triax ;
    
    //------------------------------
    //  Recycling for the next step
    //------------------------------
    
    ent_prev = ent ; 
    logn_prev = logn ; 
    dzeta_prev = dzeta ; 
    max_triax_prev = max_triax ; 
    
    fichconv << endl ;
    fichfreq << endl ;
    fichevol << endl ;
    fichconv.flush() ; 
    fichfreq.flush() ; 
    fichevol.flush() ; 

    } // End of main loop
    
    //=========================================================================
    //          End of iteration
    //=========================================================================

    ssjm1_tggg = cssjm1_tggg ; 
    ssjm1_khi = cssjm1_khi ; 
    for (int i=1; i<=3; i++) {
    ssjm1_wshift.set(i) = cssjm1_wshift(i-1) ; 
    }

    fichconv.close() ; 
    fichfreq.close() ; 
    fichevol.close() ; 

}
}