---

jiggle.C

Go to the documentation of this file.

//   version 1:  Jun 2000   Steve McMillan

#include "dyn.h"

#ifdef TOOLBOX

local void jiggle(dyn * b, real f)
{
    if (f >= 1) f = 1;

    for_all_daughters(dyn, b, bi) {

        vector vel = bi->get_vel(), norm;

        while(1) {
            real costh = randinter(-1, 1);
            real sinth = sqrt(max(0.0, 1-costh*costh));
            real phi = randinter(0, 2*M_PI);
            vector rvec = vector(sinth*cos(phi), sinth*cos(phi), costh);
            norm = rvec ^ vel;
            if (abs(norm) > 0.01*abs(vel)) break;    // norm not too close to
                                                     // being parallel to vel
        }

        // Now norm is a random vector perpendicular to vel.

        real v = abs(vel);
        vel = sqrt(1 - f*f) * vel + f * v * norm/abs(norm);
        
        bi->set_vel(vel);
    }
}

main(int argc, char ** argv)
{
    bool c_flag = false, s_flag = false;
    char *comment;
    real f = 0.01;
    int input_seed, actual_seed;
    char seedlog[128];

    check_help();

    extern char *poptarg;
    int c;
    char* param_string = "c:f:s:";

    while ((c = pgetopt(argc, argv, param_string)) != -1)
        switch(c) {

            case 'c': c_flag = true;
                      comment = poptarg;
                      break;
            case 'f': f = atof(poptarg);
                      break;
            case 's': s_flag = true;
                      input_seed = atoi(poptarg);
                      break;
            case '?': params_to_usage(cerr, argv[0], param_string);
                      get_help();
                      exit(1);
        }            

    if (!s_flag) input_seed = 0;                                // default
    actual_seed = srandinter(input_seed);

    cerr << "jiggle: random seed = " << actual_seed << endl;

    sprintf(seedlog, "       random number generator seed = %d", actual_seed);

    dyn *b;

    while (b = get_dyn(cin)) {

        b->log_history(argc, argv);
        if (c_flag) b->log_comment(comment);
        b->log_comment(seedlog);

        jiggle(b, f);
        put_dyn(cout, *b);      
        rmtree(b);
    }
}

#endif

---